Add brizental to the list of people who can sign Tor Browser and Mullvad Browser tags

Bea has worked a lot on RR rebases, but she can't tag them because her keyring isn't in the repo.

I think we should add her (/cc @morgan for confirmation, even though I already asked on IRC 😄).

@brizental could you please send a copy of your PGP public key?

Somewhere in the Internets there should be a signature I did last year in Portugal on it.