Issue #20668: Remove tests.txt of test_asyncio

It's useless, tests are now discovered automatically.
use https docs url (#21115)
merge 3.2
merge 3.3 (#21115)
use https docs url
Issue #21073: explain why Py_ReprEnter() allows for a missing thread state.
Fix the doc: add deprecation warning in select module.
IOError -> OSError
Get rid of deprecated IOError in the doc
#16716: remove deprecation warning