Switching to beta from https://musicbrainz.org/reports takes you to https://beta.musicbrainz.org/reports as expected.
Trying to switch back takes you to https://musicbrainz.org/?unset_beta=1
beta.mb→mb link (unset_beta=1) should stay on same page
make mirror server's "return to musicbrainz.org" link go to the right place
Redirect to previous page instead of home page when unsetting beta