test: add temporarily blacklisted tests
This temporarily blacklists some tests when run under Ubuntu CI.
This is the upstream side of the Debian 'upstream' test MR:
https://salsa.debian.org/systemd-team/systemd/merge_requests/52
The tests blacklisted here should only be temporarily blacklisted
until they can be fixed; the intention is that these blacklist files
will be added and removed over time while debugging/fixing flaky
and/or regressed tests, without causing test failure noise for other
PRs.