Make a double blue checkmark symbol with square contours using Ti*k*Z

\documentclass{article}
\usepackage{tikz}

\tikzset{pics/.cd, checkmark/.style={code={% 
\pgfgettransformentries{\tmpxx}{\tmp}{\tmp}{\tmp}{\tmp}{\tmp}
\draw[line width=\tmpxx*1pt,draw=none,fill=blue!60] (0,.33) -- (.25,0) to 
  (0.8,.6) to (.72,.68) to (.25,.18) to (0.08,.40)-- cycle;}}}
\tikzset{pics/.cd, clipcheckmark/.style={code={% 
\pgfgettransformentries{\tmpxx}{\tmp}{\tmp}{\tmp}{\tmp}{\tmp}
\draw[line width=\tmpxx*1pt,draw=none,fill=blue!60] (0.1,.19) -- (.25,0) to 
  (0.8,.6) to (.72,.68) to (.25,.18) to (0.18,.26)-- cycle;}}}
\newcommand{\doubleckmark}{\begin{tikzpicture}[baseline={(0,0)}]
\path (0,0) pic[scale=0.4]{checkmark} (0.16,0) pic[scale=0.4]{clipcheckmark};
\end{tikzpicture}}

\renewcommand\labelitemi{\doubleckmark}

\begin{document}

\begin{itemize}
    \item This is an item.
    \item Another item.
\end{itemize}


\end{document}

Just for fun: an attempt to obtain a precise match.

\documentclass{article}
\usepackage{scalerel}
\usepackage{tikz}
\definecolor{cmblue}{RGB}{1,126,254}
\newcommand{\doubleckmark}{\scalerel*{\begin{tikzpicture}[x=2ex,y=2ex]
\draw[line width=0.72ex,cmblue] (136:1.25) -- (0,0) -- (51:2.85);
\draw[xshift=2.5ex,line width=0.72ex,cmblue] (137:0.55) -- (0,0) -- (52:2.85);
\end{tikzpicture}}{W}}

\renewcommand\labelitemi{\doubleckmark}

\begin{document}

\begin{itemize}
    \item This is an item.
    \item Another item.
\end{itemize}
\end{document}