* bpo-30121: Fix debug assert in subprocess on Windows (#1224)

* bpo-30121: Fix debug assert in subprocess on Windows

This is caused by closing HANDLEs using os.close which is for CRT file
descriptors and not for HANDLEs.

* bpo-30121: Suppress debug assertion in test_subprocess when ran directly

(cherry picked from commit 4d385172)

* Add test_subprocess.test_nonexisting_with_pipes() (#3133)

bpo-30121: Test the Popen failure when Popen was created with pipes.
Create also NONEXISTING_CMD variable in test_subprocess.py.
(cherry picked from commit 9a83f651)