MOD: Improve mock live server teardown

Author: nmacholl

tests/conftest.py

@@ -251,11 +251,17 @@ async def fixture_mock_live_server(
 
         yield mock_live_server
 
-    loop.run_in_executor(
-        None,
-        loop.stop,
-    )
-    thread.join()
+        asyncio.run_coroutine_threadsafe(
+            coro=mock_live_server.stop(),
+            loop=loop,
+        ).result()
+
+        loop.run_in_executor(
+            None,
+            loop.stop,
+        )
+
+        thread.join()
 
 
 @pytest.fixture(name="historical_client")