* main:
  pythongh-68686: Retire eptag ptag scripts (python#98064)
  pythongh-97922: Run the GC only on eval breaker (python#97920)
  GitHub Workflows security hardening (python#96492)
  Add `@ezio-melotti` as codeowner for `.github/`. (python#98079)
  pythongh-97913 Docs: Add walrus operator to the index (python#97921)
  [doc] Fix broken links to C extensions accelerating stdlib modules (python#96914)
  pythongh-97822: Fix http.server documentation reference to test() function (python#98027)
  pythongh-91052: Add PyDict_Unwatch for unwatching a dictionary (python#98055)
  pythonGH-98023: Change default child watcher to PidfdChildWatcher on supported systems (python#98024)
  pythonGH-94182: Run the PidfdChildWatcher on the running loop (python#94184)

* main: (5519 commits)
  Minor edits to the Descriptor HowTo Guide (pythonGH-24901)
  Fix link to Lifecycle of a Pull Request in CONTRIBUTING (python#98102)
  pythonGH-94597: deprecate `SafeChildWatcher`, `FastChildWatcher` and `MultiLoopChildWatcher` child watchers  (python#98089)
  Auto-cancel old builds when new commit pushed to branch (python#98009)
  pythongh-95011: Migrate syslog module to Argument Clinic (pythonGH-95012)
  pythongh-68686: Retire eptag ptag scripts (python#98064)
  pythongh-97922: Run the GC only on eval breaker (python#97920)
  GitHub Workflows security hardening (python#96492)
  Add `@ezio-melotti` as codeowner for `.github/`. (python#98079)
  pythongh-97913 Docs: Add walrus operator to the index (python#97921)
  [doc] Fix broken links to C extensions accelerating stdlib modules (python#96914)
  pythongh-97822: Fix http.server documentation reference to test() function (python#98027)
  pythongh-91052: Add PyDict_Unwatch for unwatching a dictionary (python#98055)
  pythonGH-98023: Change default child watcher to PidfdChildWatcher on supported systems (python#98024)
  pythonGH-94182: Run the PidfdChildWatcher on the running loop (python#94184)
  pythongh-92886: make test_ast pass with -O (assertions off) (pythonGH-98058)
  pythongh-92886: make test_coroutines pass with -O (assertions off) (pythonGH-98060)
  pythongh-57179: Add note on symlinks for os.walk (python#94799)
  pythongh-94808: Fix regex on exotic platforms (python#98036)
  pythongh-90085: Remove vestigial -t and -c timeit options (python#94941)
  ...

…#94184)

There is no reason for this watcher to be attached to any particular loop.
This should make it safe to use regardless of the lifetime of the event loop running in the main thread
(relative to other loops).

Co-authored-by: Yury Selivanov <yury@edgedb.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

This is a backport from cpython 3.12

https://docs.python.org/3/library/asyncio-policy.html
> PidfdChildWatcher is a “Goldilocks” child watcher implementation. It doesn’t require signals or threads, doesn’t interfere with any processes launched outside the event loop, and scales linearly with the number of subprocesses launched by the event loop. The main disadvantage is that pidfds are specific to Linux, and only work on recent (5.3+) kernels.

python/cpython#98024
There are some additional fixes in cpython 3.12
in python/cpython#94184
when there is no event loop running in the main thread
but this is not a problem we have

This is a backport from cpython 3.12

https://docs.python.org/3/library/asyncio-policy.html
> PidfdChildWatcher is a “Goldilocks” child watcher implementation. It doesn’t require signals or threads, doesn’t interfere with any processes launched outside the event loop, and scales linearly with the number of subprocesses launched by the event loop. The main disadvantage is that pidfds are specific to Linux, and only work on recent (5.3+) kernels.

python/cpython#98024
There are some additional fixes in cpython 3.12
in python/cpython#94184
when there is no event loop running in the main thread
but this is not a problem we have

This is a backport from cpython 3.12

https://docs.python.org/3/library/asyncio-policy.html
> PidfdChildWatcher is a “Goldilocks” child watcher implementation. It doesn’t require signals or threads, doesn’t interfere with any processes launched outside the event loop, and scales linearly with the number of subprocesses launched by the event loop. The main disadvantage is that pidfds are specific to Linux, and only work on recent (5.3+) kernels.

python/cpython#98024
There are some additional fixes in cpython 3.12
in python/cpython#94184
when there is no event loop running in the main thread
but this is not a problem we have