Add type hints for tests/unittest.py. (#12347)

In particular, add type hints for get_success and friends, which are then helpful in a bunch of places.

tests/storage/databases/main/test_lock.py

@@ -28,7 +28,7 @@ class LockTestCase(unittest.HomeserverTestCase):
         """
         # First to acquire this lock, so it should complete
         lock = self.get_success(self.store.try_acquire_lock("name", "key"))
-        self.assertIsNotNone(lock)
+        assert lock is not None
 
         # Enter the context manager
         self.get_success(lock.__aenter__())
@@ -45,7 +45,7 @@ class LockTestCase(unittest.HomeserverTestCase):
 
         # We can now acquire the lock again.
         lock3 = self.get_success(self.store.try_acquire_lock("name", "key"))
-        self.assertIsNotNone(lock3)
+        assert lock3 is not None
         self.get_success(lock3.__aenter__())
         self.get_success(lock3.__aexit__(None, None, None))
 
@@ -53,7 +53,7 @@ class LockTestCase(unittest.HomeserverTestCase):
         """Test that we don't time out locks while they're still active"""
 
         lock = self.get_success(self.store.try_acquire_lock("name", "key"))
-        self.assertIsNotNone(lock)
+        assert lock is not None
 
         self.get_success(lock.__aenter__())
 
@@ -69,7 +69,7 @@ class LockTestCase(unittest.HomeserverTestCase):
         """Test that we time out locks if they're not updated for ages"""
 
         lock = self.get_success(self.store.try_acquire_lock("name", "key"))
-        self.assertIsNotNone(lock)
+        assert lock is not None
 
         self.get_success(lock.__aenter__())