Use HTTPStatus constants in place of literals in tests. (#13297)

changelog.d/13297.misc

tests/federation/test_complexity.py

tests/federation/test_federation_server.py

tests/federation/transport/test_knocking.py

tests/handlers/test_password_providers.py

tests/rest/admin/test_user.py

tests/rest/client/test_account.py

tests/rest/client/test_login.py

tests/rest/client/test_rooms.py