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

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