[Tails-l10n] Release schedule for Tails 4.20

Hi,

Our next release, 4.20, is scheduled for July 13.
anonym will be the Release Manager.

So:

- Dear manual testers, please let anonym know how much manual testing
you can do on July 12 (evening CEST) and July 13 (morning CEST).

- anonym, please bootstrap the release process and ensure you have
scheduled the next steps.

There's a good chance there will also be a 4.20~rc1 at some point,
which I hope we'll schedule on Thursday.

Cheers!