bpo-33929: multiprocessing: fix handle leak on race condition (GH-7921)

bpo-33929: multiprocessing: fix handle leak on race condition (GH-7921)

Fix a race condition in Popen of
multiprocessing.popen_spawn_win32. The child process now duplicates
the read end of pipe instead of "stealing" it.

Previously, the read end of pipe was "stolen" by the child process,
but it leaked a handle if the child process had been terminated
before it could steal the handle from the parent process.
(cherry picked from commit 2cc9d21fffb8146d30e6fb4221e32410ba4b4ab7)

Co-authored-by: Victor Stinner <vstinner@redhat.com>