bpo-28087: Skip test_asyncore and test_eintr poll failures on macOS. (#462) (#973)

* bpo-28087: Skip test_asyncore and test_eintr poll failures on macOS

Skip some tests of select.poll when running on macOS due to unresolved
issues with the underlying system poll function on some macOS versions.

(cherry picked from commit de04644627f82d9dc48b3423def7ff5b4aa1926a)
2 files changed