[3.10] bpo-40882: Fix a memory leak in SharedMemory on Windows (GH-20684)

In multiprocessing.shared_memory.SharedMemory(), the temporary view
returned by MapViewOfFile() should be unmapped when it is no longer
needed..
(cherry picked from commit 85c128e)

Co-authored-by: Zackery Spytz <[email protected]>

Author: lukegarland