bpo-46913: test_hashlib skips _sha3 tests on UBSan (GH-31673)

If Python is built with UBSan, test_hashlib skips tests on the _sha3
extension which currently has undefined behaviors.

This change allows to run test_hashlib to check for new UBSan regression,
but the known _sha3 undefined behavior must be fixed.
1 file changed