Python mtime timestamp logic does not work well with ostree force 0
mtime.
Use a small script to post-process all compiled '.pyc' and force the
timestamp to 0.
See: https://github.com/ostreedev/ostree/issues/1469
Co-Authored-By: Miro Hrončok <miro@hroncok.cz>
Bash Heredoc in inline YAML string is tricky. Use an independent
post-process script instead.
Fixes: 5bbc140 Revert "Revert "common: Add readonly sysroot migration unit and script""