Use inline type hints in `tests/` (#10350)

This PR is tantamount to running:

    python3.8 -m com2ann -v 6 tests/

(com2ann requires python 3.8 to run)

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/util/caches/test_descriptors.py b/tests/util/caches/test_descriptors.py

index 0277998cbe..39947a166b 100644
--- a/tests/util/caches/test_descriptors.py
+++ b/tests/util/caches/test_descriptors.py
@@ -174,7 +174,7 @@ class DescriptorTestCase(unittest.TestCase):
                 return self.result
 
         obj = Cls()
-        callbacks = set()  # type: Set[str]
+        callbacks: Set[str] = set()
 
         # set off an asynchronous request
         obj.result = origin_d = defer.Deferred()