Refleaks in multiple buildbots for test_capi, test_embed, test_import, test_interpreters, test_json and more

[pablogsal]

Bug report

Bug description:

See for example:

https://buildbot.python.org/all/#/builders/259/builds/2043

10 slowest tests:
- test.test_multiprocessing_spawn.test_processes: 5 min 50 sec
- test.test_concurrent_futures.test_wait: 5 min 3 sec
- test_fstring: 4 min 53 sec
- test.test_multiprocessing_forkserver.test_processes: 4 min 46 sec
- test_socket: 4 min 40 sec
- test.test_multiprocessing_spawn.test_misc: 3 min 34 sec
- test_io: 3 min 33 sec
- test_regrtest: 3 min 26 sec
- test_signal: 3 min 5 sec
- test_subprocess: 3 min 1 sec
16 tests skipped:
    test.test_asyncio.test_windows_events
    test.test_asyncio.test_windows_utils test_android test_apple
    test_devpoll test_free_threading test_ioctl test_kqueue
    test_launcher test_msvcrt test_startfile test_winapi
    test_winconsoleio test_winreg test_winsound test_wmi
4 tests skipped (resource denied):
    test_peg_generator test_tkinter test_ttk test_zipfile64
8 re-run tests:
    test_capi test_embed test_import test_interpreters test_json
    test_logging test_sysconfig test_zoneinfo
8 tests failed:
    test_capi test_embed test_import test_interpreters test_json
    test_logging test_sysconfig test_zoneinfo
456 tests OK.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-129271: Fix reference leak with unicode writer in fast path in the json module #129272