gh-110918: Fix side effects of regrtest test_match_tests()

[vstinner]

test_match_tests now saves and restores patterns.

Add get_match_tests() function to libregrtest.filter.

Previously, running test_regrtest multiple times in a row only ran tests once: "./python -m test test_regrtest -R 3:3.

• Issue: regrtest: allow to intermix --match and --ignore options #110918

[vstinner]

Example: https://buildbot.python.org/all/#/builders/259/builds/1062

./python -E  -m test --slow-ci --timeout=12000 -R 3:3 -u-cpu -j10 
+ ./python -u -W default -bb -E -m test --slow-ci --timeout=12000 -R 3:3 -u-cpu -j10 --dont-add-python-opts
(...)
0:11:44 load avg: 16.09 [392/472/1] test_regrtest ran no tests (36.2 sec) -- running (7): test_socket (2 min 40 sec), test.test_concurrent_futures.test_wait (54.8 sec), test_imaplib (8 min 37 sec), test.test_multiprocessing_forkserver.test_processes (3 min 5 sec), test.test_multiprocessing_spawn.test_misc (1 min 47 sec), test_zipfile (1 min 31 sec), test_io (2 min 59 sec)
beginning 6 repetitions. Showing number of leaks (. for 0 or less, X for 10 or more)
123:456
(...)
Ran 111 tests in 35.743s

OK (skipped=2)
X
----------------------------------------------------------------------
Ran 0 tests in 0.000s

NO TESTS RAN

[miss-islington-app]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-116726 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-116727 is a backport of this pull request to the 3.11 branch.