gh-121621: Move asyncio_running_loop to private struct

[colesbury]

This avoids changing the ABI and places the field in the private struct.

• Issue: asyncio module state should be locked with mutexes in free-threaded builds #121621

[colesbury]

I don't know if we care enough about avoiding ABI changes in 3.13. If not, then feel free to close this PR.

[JelleZijlstra]

I don't know much about this area, but it seems better in any case to put this element on a private struct if we don't need it to be public.

[Yhg1s]

Considering ABI stability is of great benefit for testing, and this doesn't seem like an otherwise onerous change, I'd prefer to get this in. We need to delay 3.13b4 until tomorrow anyway because of unrelated issues, so I'll respin with this in.

[miss-islington-app]

Thanks @colesbury for the PR, and @Yhg1s for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-121943 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x Fedora Clang Installed 3.13 has failed when building commit afa5321.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#builders/1392/builds/212) and take a look at the build logs.
4. Check if the failure is related to this commit (afa5321) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#builders/1392/builds/212

Failed tests:

• test_pyrepl

Failed subtests:

• test_inspect_keeps_globals_from_inspected_file - test.test_pyrepl.test_pyrepl.TestMain.test_inspect_keeps_globals_from_inspected_file
• test_inspect_keeps_globals_from_inspected_module - test.test_pyrepl.test_pyrepl.TestMain.test_inspect_keeps_globals_from_inspected_module

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.13.edelsohn-fedora-z.clang-installed/build/target/lib/python3.13/test/test_pyrepl/test_pyrepl.py", line 995, in _run_repl_globals_test
    self.fail(f"{var}= not found in output")
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: FOO= not found in output


Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.13.edelsohn-fedora-z.clang-installed/build/target/lib/python3.13/test/test_pyrepl/test_pyrepl.py", line 995, in _run_repl_globals_test
    self.fail(f"{var}= not found in output")
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: __name__= not found in output


Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.13.edelsohn-fedora-z.clang-installed/build/target/lib/python3.13/test/test_pyrepl/test_pyrepl.py", line 995, in _run_repl_globals_test
    self.fail(f"{var}= not found in output")
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: __package__= not found in output