This commit fixes a bug in maint/adhoc-add-lint-blocks, which made it
impossible to execute, because `/usr/bin/env` looked at Perl's command
line arguments to be a part of the binary name.
This commit changes the shebang in all shell scripts from absolute
paths (such as `/bin/bash` or `/usr/bin/python3`) to the `/usr/bin/env`
binary with the accompanying interpreter as it's argument.
The reason for this are as follows:
- NixOS cannot work with absolute paths
- BSD systems install their packages in /usr/local/bin