Reset counter within a \newtcbinputlisting environment

Use the number within key of the init (i.e. bootstrap) section of a \newtcblisting box, i.e. the first optional argument -- don't confuse it with the options that are given to the real tcblisting environment later on.

i.e \newtcblisting[use counter=foo,number within=chapter]{...}

\documentclass[a4paper, 10pt]{book}

\newcommand{\codeimg}{\includegraphics[scale=0.1]{example-image-a}}

\newcounter{datacounter}[chapter]


\usepackage{calc}
\usepackage[usenames,dvipsnames,svgnames,table]{xcolor}
\usepackage{pdfpages,graphicx}
\usepackage{listings}
\usepackage{filecontents}
\usepackage[numbered,framed]{matlab-prettifier}

\definecolor{light-gray}{gray}{0.92}
\definecolor{myblueiii}{RGB}{199,234,253}
\definecolor{mainColor}{RGB}{211, 47, 47} % some dark red
\definecolor{codegreen}{rgb}{0,0.6,0}
\definecolor{codegray}{rgb}{0.5,0.5,0.5}
\definecolor{codepurple}{rgb}{0.58,0,0.82}
\definecolor{backcolour}{rgb}{0.95,0.95,0.92}
\definecolor{mybluei}{RGB}{0,173,239}
\definecolor{myblueiii}{RGB}{199,234,253}

\lstdefinestyle{mycode}{
    language=Python,
    numbers=left,
    numbersep= 10mm,
    numberstyle=\color{Black},
    stepnumber=1,
    tabsize=3,
    breakatwhitespace=false,
    breaklines=true,
    captionpos=b,
    basicstyle=\color{Black}\ttfamily,
    commentstyle=\color{LimeGreen},
    keywordstyle=\color{BurntOrange}\bfseries,
    stringstyle=\color{WildStrawberry},
    keywords={var, func, extends},
    frame=leftline,
    framesep=0mm,
    xleftmargin=3mm,
    framesep=2mm,
    framerule=0mm,
    abovecaptionskip=5mm,
    aboveskip=\baselineskip,
    belowskip=\baselineskip
}

\usepackage{tcolorbox}
\newcounter{data}
\newcounter{result}
\newcounter{pythoncode}
\newcounter{matlab}
\tcbuselibrary{skins,breakable,listings}
\newtcblisting[use counter=pythoncode,number within=chapter]{codeblock}[2][]{%listing options={style=mycode},%
        enhanced,noparskip,breakable,colback=light-gray,colframe=DarkSlateGray,opacitybacktitle=.8,%
        fonttitle=\bfseries,before upper={\hspace*{-1em}\includegraphics[height=\baselineskip]{example-image-a}~#2},%
        title after break={\centering\footnotesize\itshape\strut Python Code~\thechapter.\thepythoncode~--~continued},%
        listing only,listing options={xleftmargin=-1mm,#1,style=mycode},after upper={\centering\strut Python Code~\thechapter.\thepythoncode:~#2},
        frame hidden,arc=0pt,outer arc=0pt,boxrule=0pt,frame code={\draw[gray,line width=2mm] ([xshift=-0.5pt]frame.north west) -- ([xshift=-0.5pt]frame.south west);},#1}
\newtcbinputlisting[use counter=data,number within=chapter]{\inputdata}[3][]{%listing options={style=weka},%
    title after break={\centering\footnotesize\itshape\strut Data~\thechapter.\thedata~--~continued},%
     listing only,listing options={xleftmargin=-1mm,#1,style=weka},after upper={\centering\strut Data~\thechapter.\thedata:~#2},%
     listing file={#3}}
\newtcbinputlisting[use counter=result,number within=chapter]{\inputresult}[3][]{%listing options={style=mystyleresults},%
enhanced,noparskip,breakable,colback=myblueiii,opacitybacktitle=.8,%
    title after break={\centering\footnotesize\itshape\strut Result~\thechapter.\theresult~--~continued},%
     listing only,listing options={xleftmargin=-1mm,#1,style=mystyleresults},after upper={\centering\strut Result~\thechapter.\theresult:~#2},%
     listing file={#3}}
\newtcbinputlisting[use counter=matlab,number within=chapter]{\inputmatlab}[3][]{%listing options={style=Matlab-editor},%
    title after break={\centering\footnotesize\itshape\strut Matlab Code~\thechapter.\thematlab~--~continued},%
     listing only,listing options={xleftmargin=-1mm,#1,style=Matlab-editor},after upper={\centering\strut Matlab Code~\thechapter.\thematlab:~#2},%
     listing file={#3}}

\lstdefinestyle{mystyleresults}{
    commentstyle=\color{codegreen},
    keywordstyle=\color{black},
    numberstyle=\tiny\color{codegray},
    stringstyle=\color{black},
    basicstyle=\ttfamily\footnotesize,
    breakatwhitespace=false,
    breaklines=true,
    captionpos=b,
    keepspaces=true,
    numbers=none,
    numbersep=5pt,
    showspaces=false,
    showstringspaces=false,
    showtabs=false,
    tabsize=6
}

\lstdefinestyle{weka}{
    %backgroundcolor=\color{DarkSlateGray},
    numbers=none,
    numbersep=5pt,
    numberstyle=\tiny\color{codegray},
    commentstyle=\color{codegreen},
    keywordstyle=\color{blue},
    keywordstyle={[2]\color{magenta}},
    stringstyle=\color{codepurple},
    basicstyle=\footnotesize,
    comment=[l]{\%},
    keywords={@relation,@attribute,@data},
    morekeywords=[2]{real,integer,numeric,string,date},
    breakatwhitespace=false,
    breaklines=true,
    captionpos=b,
    keepspaces=true,
    showspaces=false,
    showstringspaces=false,
    showtabs=false,
    tabsize=2
}

\begin{filecontents}{result1.txt}
=== Run information ===

Correlation coefficient                  0.5941
Mean absolute error                      2.2173
Root mean squared error                  3.7905
Relative absolute error                 76.7091 %
Root relative squared error             81.3406 %
Total Number of Instances              188

\end{filecontents}

\begin{filecontents}{result2.txt}
% 9 attributes
% 188 instances

@relation FIT

@attribute NUMUORS real   % Number of unique operators
@attribute NUMUANDS real  % Number of unique operands
@attribute TOTOTORS real  % Total number of operators

\end{filecontents}

\begin{filecontents*}{sample.m}
% create a file for output
!touch testFile.txt
fid = fopen('testFile.text', 'w')
for i=1:10
  fprintf(fid,'%6.2f \n', i);
end
\end{filecontents*}


\begin{document}
\chapter{Data}
\section{Data1}
\inputdata{Code Snippet}{result2.txt}
\inputdata{Code Snippet}{result2.txt}
\inputresult{Result from run 1}{result1.txt}

\begin{codeblock}{Les bases de GDScript}
var nombreDeGardes = 4 #déclaration d'une variable
nombreDeGardes = plusDeux(nombreDeGardes) #appel d'une fonction avec la variable nombreDeGardes passée en paramètre
\end{codeblock}

\inputmatlab{Sample matlab code}{sample.m}

\chapter{Analysis}
\section{Data2}
\inputdata{Code Snippet}{result2.txt}
\inputdata{Code Snippet}{result2.txt}
\inputresult{Result from run 1}{result1.txt}
\end{document} 

You introduce a counter you never use (datacounter) which is not necessary.

Probably you should switch to the chngcntr package. Then you could write (instead of the current counter definitions):

\usepackage{chngcntr}
\newcounter{data}\counterwithin{data}{chapter}
\newcounter{result}\counterwithin{result}{chapter}
\newcounter{pythoncode}\counterwithin{pythoncode}{chapter}
\newcounter{matlab}\counterwithin{matlab}{chapter}

Alternatively you could avoid extra packages and use

\makeatletter
\newcounter{data}\@addtoreset{data}{chapter} % equals \newcounter{data}[chapter]
\newcounter{result}\@addtoreset{result}{chapter} % equals \newcounter{result}[chapter]
\newcounter{pythoncode}\@addtoreset{pythoncode}{chapter} % equals \newcounter{pythoncode}[chapter]
\newcounter{matlab}\@addtoreset{matlab}{chapter} % equals \newcounter{matlab}[chapter]
\makeatother

And the third way (suggested by @clemens): Using amsmath and \numberwithin:

\usepackage{amsmath}
\newcounter{data}\numberwithin{data}{chapter}
\newcounter{result}\numberwithin{result}{chapter}
\newcounter{pythoncode}\numberwithin{pythoncode}{chapter}
\newcounter{matlab}\numberwithin{matlab}{chapter}