Fix codestyle CI from #10440 (#10511)

Co-authored-by: Erik Johnston <erik@matrix.org>

changelog.d/10511.feature

+Allow setting transaction limit for database connections.

tests/storage/test_txn_limit.py

@@ -32,5 +32,5 @@ class SQLTransactionLimitTestCase(unittest.HomeserverTestCase):
         db_pool = self.hs.get_datastores().databases[0]
 
         # force txn limit to roll over at least once
-        for i in range(0, 1001):
+        for _ in range(0, 1001):
             self.get_success_or_raise(db_pool.runInteraction("test_select", do_select))