gh-108638: Fix tests when _stat extension is missing

[vstinner]

Fix test_inspect and test_pydoc when the _stat extension is missing. Skip tests relying on _stat when _stat is missing.

• Issue: Test suite expects _stat extension to be available #108638

[vstinner]

I don't think that it's worth it to backport this change, it's mostly needed by PyPy which has no _stat module. In CPython, the _stat extension should always be available.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 Fedora Stable LTO + PGO 3.x has failed when building commit c6d5613.

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/all/#builders/524/builds/4351) and take a look at the build logs.
4. Check if the failure is related to this commit (c6d5613) 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/all/#builders/524/builds/4351

Failed tests:

• test.test_concurrent_futures.test_shutdown

Failed subtests:

• test_interpreter_shutdown - test.test_concurrent_futures.test_shutdown.ProcessPoolSpawnProcessPoolShutdownTest.test_interpreter_shutdown

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

== Tests result: FAILURE then FAILURE ==

446 tests OK.

10 slowest tests:

• test.test_concurrent_futures.test_wait: 1 min 10 sec
• test_signal: 1 min 4 sec
• test.test_multiprocessing_spawn.test_processes: 52.8 sec
• test_socket: 49.6 sec
• test_subprocess: 47.3 sec
• test.test_multiprocessing_forkserver.test_processes: 42.4 sec
• test_io: 38.3 sec
• test.test_multiprocessing_spawn.test_misc: 34.4 sec
• test_imaplib: 31.3 sec
• test.test_asyncio.test_tasks: 28.8 sec

1 test failed:
test.test_concurrent_futures.test_shutdown

15 tests skipped:
test.test_asyncio.test_windows_events
test.test_asyncio.test_windows_utils test_devpoll test_gdb
test_ioctl test_kqueue test_launcher test_startfile test_tkinter
test_ttk test_winconsoleio test_winreg test_winsound test_wmi
test_zipfile64

1 re-run test:
test.test_concurrent_futures.test_shutdown

Total duration: 1 min 15 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/test/test_concurrent_futures/test_shutdown.py", line 49, in test_interpreter_shutdown
    self.assertFalse(err)
AssertionError: b'Exception in thread Thread-1:\nTraceback (most recent call last):\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/threading.py", line 1059, in _bootstrap_inner\n    self.run()\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/concurrent/futures/process.py", line 339, in run\n    self.add_call_item_to_queue()\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/concurrent/futures/process.py", line 394, in add_call_item_to_queue\n    self.call_queue.put(_CallItem(work_id,\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/multiprocessing/queues.py", line 94, in put\n    self._start_thread()\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/multiprocessing/queues.py", line 177, in _start_thread\n    self._thread.start()\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/threading.py", line 978, in start\n    _start_new_thread(self._bootstrap, ())\nRuntimeError: can\'t create new thread at interpreter shutdown\nTraceback (most recent call last):\n  File "<string>", line 1, in <module>\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/multiprocessing/spawn.py", line 122, in spawn_main\n    exitcode = _main(fd, parent_sentinel)\n               ^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/multiprocessing/spawn.py", line 132, in _main\n    self = reduction.pickle.load(from_parent)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-aarch64.lto-pgo/build/Lib/multiprocessing/synchronize.py", line 115, in __setstate__\n    self._semlock = _multiprocessing.SemLock._rebuild(*state)\n                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\nFileNotFoundError: [Errno 2] No such file or directory\n' is not false