Updater is disabled when tor-browser is run by torbrowser-launcher flatpak

It looks like Tor Browser updater is disabled when run from the Flatpak version of torbrowser-launcher:

• https://github.com/torproject/torbrowser-launcher/issues/721#issuecomment-1824742227
• https://searchfox.org/mozilla-central/source/toolkit/mozapps/update/AppUpdater.sys.mjs#404

This is probably what we want when we'll have a Tor Browser Flatpak, but not for the torbrowser-launcher Flatpak.