style: fix trailing blank lines in test files

tests/core/network/test_notifee_performance.py

@@ -80,4 +80,3 @@ async def test_slow_notifee_does_not_block_others() -> None:
         with trio.fail_after(0.3):
             for ev in fast_events:
                 await ev.wait()
-

tests/core/pubsub/test_pubsub_notifee_integration.py

@@ -88,5 +88,3 @@ async def test_blacklist_blocks_peer_added_by_notifee():
         # Give handler a chance to run
         await trio.sleep(0.1)
         assert p1.my_id not in p0.peers
-
-