Fix issue with Callable, Union, and Python 3.9 [mqtt] (home-assistant…

…#83547)

homeassistant/components/mqtt/client.py

@@ -1,16 +1,19 @@
 """Support for MQTT message handling."""
+# pylint: disable=deprecated-typing-alias
+#   In Python 3.9.0 and 3.9.1 collections.abc.Callable
+#   can't be used inside typing.Union or typing.Optional
 from __future__ import annotations
 
 import asyncio
-from collections.abc import Callable, Coroutine, Iterable
+from collections.abc import Coroutine, Iterable
 from functools import lru_cache, partial, wraps
 import inspect
 from itertools import groupby
 import logging
 from operator import attrgetter
 import ssl
 import time
-from typing import TYPE_CHECKING, Any, Union, cast
+from typing import TYPE_CHECKING, Any, Callable, Union, cast
 import uuid
 
 import attr