19474 confidential symlink attack

See merge request boyska/tails!1

It fits better below /run than below /var/lib and this avoids that we
have to make /var/lib/tails-persistent-storage traversable by everyone
(/run already is).

... by using the nosymfollow mount point when accessing files controlled
by amnesia.

Closes #19474

Test new tps functionality

Closes #19225

See merge request tails/tails!1052

Test suite improvements

Closes #19420

See merge request tails/tails!1061

Upgrade to Linux 6.1.12-1 from sid (stable branch)

Closes #19456, #19398, and #19444

See merge request tails/tails!1062

Enable non-free-firmware archive area for distributions that support it

Closes #19456, #19398, and #19411

See merge request tails/tails!1036

We decided that developers who want to do different things in the hook
when running in test suite can check for the "unmount" and
"autotest_never_use_this_option".

refs #19237

The original child method already has regex support, we don't need to
implement it ourselves.

The step was failing on my system because a few pixels are missing on
the bottom of the screen keyboard.

Those are printed repeatedly so often that it's too much noise.

To be able to find the method definition via IDE navigation.

This also drops some unused methods.

The test suite changes of this commit require the updates to
tails-autotest-remote-shell from commit
"Test Suite: Fix Dogtail not working when running as Debian-gdm user"
to work. That causes some scenarios of the
"Upgrading an old Tails USB installation" feature to fail, because the
old version of Tails used by that test does not have the updates to
tails-autotest-remote-shell yet.

To avoid that, lets wait until the next release and then revert this
commit again.

In one scenario, the next step after this one was to shut down, which
caused a race: Because the step did wait until deactivation completed,
sometimes the feature was not deactivated yet, causing it to be active
again after reboot.

Closes #19420

Clicking on screenshots is flaky, both locally and in Jenkins. Using
Dogtail should be more robust.

Changing the config of 'dogtail.config' doesn't have any effect on the
config of 'dogtail.tree'. To do that, 'dogtail.tree.config' needs to be
changed.

We decided to add a --extra-boot-options to run_test_suite instead.

This allows us to inspect the journal and do other things as root when
debugging test failures in the VM.

When importing "dogtail.tree" when the AT SPI bus was inaccessible, the
Python process was terminated via SIGTRAP:

    (.:3116166): dbind-ERROR **: 14:35:52.927: AT-SPI: Couldn't connect to accessibility bus. Is at-spi-bus-launcher running?

That was hard to debug because we didn't print the stderr of the failed
Python command. With this commit, failures like the one above should be
a lot easier to debug.

Handle exceptions during JSON decoding by returning the exception to the
caller instead of letting the Remote Shell exit abruptly which makes
things hard to debug.