[tlbuild] Broken shebangs in TeX Live scripts

[Bruno Haible]

> > I cannot conceive of a
> > linux system where some form of /bin/bash does not exist.
> 
> NixOS does not have /bin/bash

GNU guix does not have /bin/bash either. It has only /bin/sh (because that
is mandated by POSIX) and /usr/bin/env. All other programs are available
in other directories listed in $PATH.

> > > $ 2>/dev/null grep '^#!' /opt/texlive/2022/bin/x86_64-linux/* |
> > > grep -v -e '/usr/bin/env' -e '/bin/sh'

Yup. All these findings are problematic.

Bruno