* 'master' of https://github.com/python/cpython: (601 commits)
  remove check for bug last seem in Solaris 9 (python#3285)
  Change code owners for hashlib and ssl to the crypto team (python#3284)
  bpo-31281: Fix pathlib.Path incompatibility in fileinput (pythongh-3208)
  remove autoconf check for select() (python#3283)
  remove configure check for 'volatile' (python#3281)
  Add missing _sha3 module to Setup.dist (python#2395)
  bpo-12383: Also ignore __PYVENV_LAUNCHER__ (python#3278)
  bpo-9146: add the missing NEWS entry. (python#3275)
  Fix a c.f.as_completed() refleak previously introduced in bpo-27144 (python#3270)
  bpo-31185: Fixed miscellaneous errors in asyncio speedup module. (python#3076)
  remove a redundant lower in urllib.parse.urlsplit (python#3008)
  bpo-31323: Fix reference leak in test_ssl (python#3263)
  bpo-31250, test_asyncio: fix EventLoopTestsMixin.tearDown() (python#3264)
  bpo-31326: ProcessPoolExecutor waits for the call queue thread (python#3265)
  bpo-27144: concurrent.futures as_complete and map iterators do not keep reference to returned object (python#1560)
  bpo-31250, test_asyncio: fix dangling threads (python#3252)
  bpo-31217: Fix regrtest -R for small integer (python#3260)
  bpo-30096: Use ABC in abc reference examples (python#1220)
  bpo-30737: Update DevGuide links to new URL (pythonGH-3228)
  [Trivial] Remove now redundant assert (python#3245)
  ...

)

Call doCleanups() to close the loop after calling
executor.shutdown(wait=True): see TestCase.set_event_loop() of
asyncio.test_utils.

Replace also gc.collect() with support.gc_collect().

* bpo-31250, test_asyncio: fix dangling threads (#3252)

* Explicitly call shutdown(wait=True) on executors to wait until all
  threads complete to prevent side effects between tests.
* Fix test_loop_self_reading_exception(): don't mock loop.close().
  Previously, the original close() method was called rather than the
  mock, because how set_event_loop() registered loop.close().

(cherry picked from commit 16432be)

* bpo-31250, test_asyncio: fix EventLoopTestsMixin.tearDown() (#3264)

Call doCleanups() to close the loop after calling
executor.shutdown(wait=True): see TestCase.set_event_loop() of
asyncio.test_utils.

Replace also gc.collect() with support.gc_collect().

(cherry picked from commit e8a533f)