snap-policy: ensure audio works with .deb snapd
requested to merge sergio-costas/pipewire-fork:snap-policy-manage-all-cases-for-snapd-installation into master
When snapd is installed as a .deb instead of a snap, its slots are identified as 'core:XXXX' instead of 'snapd:XXXX'. The current code doesn't take this into account, so those users that have snapd installed from a .deb package instead of running an updated version in snap form will have problems with audio.
This patch fixes this.