standard_init_linux.go:211: exec user process caused "no such file or directory"?

The "shebang" line at the start of a script says what interpreter to use to run it. In your case, your script has specified #!/bin/bash, but Alpine-based Docker images don't typically include GNU bash; instead, they have a more minimal /bin/sh that includes just the functionality in the POSIX shell specification.

Your script isn't using any of the non-standard bash extensions, so you can just change the start of the script to

#!/bin/sh

This can also happen if the line endings of the script is wrong, i.e. \r\n instead of \r

this can be checked using the file path/to/script.sh command which tells if the script has CR-LF line endings

If its a one off script dos2unix can be used to change it to \r\n to \n

If its a git repository setting the autocrlf option to input would work

How to change line-ending settings