Add regression tests
As a first pass, adding a basic regression test for whether emulators start would be useful.
Ideally, they would be callable from gnome-games for use as a regression test when building the Flatpak (see "GLib installed tests").
To being with, Game Boy games should be able to start, including those start ROMs: https://github.com/Gekkio/mooneye-gb
See also: https://sameboy.github.io/automation/