Avoid dangling task-local connections after Database.disconnect() (#211)

Co-authored-by: Amin Alaee <[email protected]>

Author: vmarkovtsev

databases/core.py

@@ -118,6 +118,8 @@ async def disconnect(self) -> None:
 
             self._global_transaction = None
             self._global_connection = None
+        else:
+            self._connection_context = contextvars.ContextVar("connection_context")
 
         await self._backend.disconnect()
         logger.info(