Zero out mtime when commiting
Zero out mtime when commiting

This means we get the same behaviour as if we checked out of
the cache. Also, its the same as the final behaviour will be
when running in flatpak.

flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,GeorgesStavracas/flatpak,flatpak/flatpak,GeorgesStavracas/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,GeorgesStavracas/flatpak,matthiasclasen/flatpak,GeorgesStavracas/flatpak,GeorgesStavracas/flatpak,handsome-feng/flatpak,amigadave/flatpak,amigadave/flatpak,handsome-feng/flatpak,amigadave/flatpak,handsome-feng/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,amigadave/flatpak,flatpak/flatpak