Draft: build/linux: Use custom App ID on Testing AppImage and Nightly flatpak
This is a common pratice in GNOME nightly apps and should workaround the fact the DEs are very dumb and confuse different GIMPs if they don't have different APP IDs.
This is a common pratice in GNOME nightly apps and should workaround the fact the DEs are very dumb and confuse different GIMPs if they don't have different APP IDs.