bpo-36234: Add more tests to PosixUidGidTests (GH-12234)

test_posix.PosixUidGidTests:

* Add tests for invalid uid/gid type (str)
* Add UID_OVERFLOW and GID_OVERFLOW constants to replace (1 << 32)

Initial patch written by David Malcolm.

Co-Authored-By: David Malcolm <dmalcolm@redhat.com>
2 files changed