If config/APT_overlays.d is empty, then the earlier command will
delete the .placeholder file and we lose the directory.

It was deleted by `./bin/merge-APT-overlays stable` which is wrong.

Thunderbird 78 and Enigmail obsoletion

Closes #17148 and #17147

See merge request tails/tails!203

Tor Browser 10.0.5

Closes #18017, #18016, and #17139

See merge request tails/tails!253

It's fixed in Tor Browser 10.0.5.

Release process: streamline configuration and environment management

See merge request tails/tails!245

At least the "X in the address bar" part was not robust; I saw it fail
several times, presumably because right when it tested the correct
image the blinking cursor was visible, preventing a match.

Since we known which image should match, let's just do that instead.

This is a follow-up on #18016 and !251, which had not been tested with
a full test suite run. :)

Thanks @anonym for the suggestion!

Fixes regression introduced by 48f39fb4

Browsers: drop el-GR from browser localization

Closes #18015

See merge request tails/tails!252

Test suite: wait for GNOME Overview launchers to be ready before interacting with them

Closes #18016

See merge request tails/tails!251

Merge remote-tracking branch 'origin/test/18016-gnome-overview-robustness' into feature/18017-tor-browser-10.0.5+force-all-tests

Closes: #18016

Merge remote-tracking branch 'origin/test/17139-drop-el-GR-browser-localization' into feature/18017-tor-browser-10.0.5+force-all-tests

Closes: #17139

Closes: #18017