Fix-up bad import.

Author: clokep

tests/appservice/test_scheduler.py

@@ -17,6 +17,7 @@
 from typing_extensions import TypeAlias
 
 from twisted.internet import defer
+from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.appservice import (
     ApplicationService,
@@ -40,9 +41,6 @@
 
 from ..utils import MockClock
 
-if TYPE_CHECKING:
-    from twisted.internet.testing import MemoryReactor
-
 
 class ApplicationServiceSchedulerTransactionCtrlTestCase(unittest.TestCase):
     def setUp(self) -> None: