[Tails-l10n] Release schedule for Tails 4.28

Hi,

Tails 4.28 should be released on March 8.

At this point we don't know who the Release Manager for that release
will be.

Dear manual testers, please let tails-rm@??? know
_how much_ manual testing you do on March 7 (evening CET)
and March 8 (morning CET). Thanks in advance!

Cheers!