Add stubtest allowlist entry

Author: srittau

stdlib/@tests/stubtest_allowlists/common.txt

@@ -234,6 +234,7 @@ asyncio.locks.Condition.acquire
 asyncio.locks.Condition.locked
 asyncio.locks.Condition.release
 
+builtins.function  # stubtest believes this exists in the stubs when it doesn't
 builtins.memoryview.__contains__  # C type that implements __getitem__
 builtins.reveal_locals  # Builtins that type checkers pretends exist
 builtins.reveal_type  # Builtins that type checkers pretends exist