This cleans up the GitHub actions yaml a bit and ensures that developers
are running this check locally before submitting changes. In addition,
it allows adding tests for this check. Finally, this change fixes the
tidy tests by upgrading voluptuous for Python 3.10 as well as by
reverting an inadvertent change for NixOS compatibility on one of the
dummy testing files.
This changes tidy to check shell scripts for the proper shebang and
options. It does not check that variables are formatted correctly. It
also adds a check for the MPL 2.0 license in shell scripts.