Actually typecheck tests.test_server

Missed from #13124.

Author: David Robertson

mypy.ini

@@ -56,7 +56,6 @@ exclude = (?x)
    |tests/server.py
    |tests/server_notices/test_resource_limits_server_notices.py
    |tests/test_metrics.py
-   |tests/test_server.py
    |tests/test_state.py
    |tests/test_terms_auth.py
    |tests/util/caches/test_cached_call.py