Fix memory leaks in test_capi

[carljm]

These memory leaks were recently introduced in #31787. Not sure if this fix qualifies as "trivial" or requires an issue also.

Before this fix, ./python -m test test_capi -R 3:3 reports a memory leak; after this fix it passes.

[kumaraditya303]

@kumaraditya303 ➜ /workspaces/cpython (fixleak) $ ./python -m test test_capi -R 3:3
0:00:00 load avg: 0.98 Run tests sequentially
0:00:00 load avg: 0.98 [1/1] test_capi
beginning 6 repetitions
123456
......
test_capi passed in 38.6 sec

== Tests result: SUCCESS ==

1 test OK.

Total duration: 38.6 sec
Tests result: SUCCESS

[kumaraditya303]

@vstinner: This PR fixes ref leak on main. Currently all refleak buildbots are failing. See https://buildbot.python.org/all/#/release_status

[vstinner]

You may want to use test.support.catch_unraisable_exception context manager, but it only stores the latest unraisable exception.

[carljm]

Thanks @vstinner, included the switch to catch_unraisable_exception in #98055

[vstinner]

Thanks @vstinner, included the switch to catch_unraisable_exception in #98055

Thanks! I like the new test code.