Import iscoroutinefunction() from inspect rather than asyncio

The asyncio function is deprecated starting from Python 3.14 and
will be removed from Python 3.16.

Author: befeleme

Diff for: vcr/cassette.py

@@ -3,7 +3,7 @@
 import copy
 import inspect
 import logging
-from asyncio import iscoroutinefunction
+from inspect import iscoroutinefunction
 
 import wrapt