Replace asyncio.iscoroutinefunction with inspect.iscoroutinefunction

DeprecationWarning: 'asyncio.iscoroutinefunction' is deprecated and slated for removal in Python 3.16; use inspect.iscoroutinefunction() instead

Fixes #468

src/pytest_mock/plugin.py

@@ -1,4 +1,3 @@
-import asyncio
 import builtins
 import functools
 import inspect
@@ -196,7 +195,7 @@ async def async_wrapper(*args, **kwargs):
                 spy_obj.spy_return_list.append(r)
             return r
 
-        if asyncio.iscoroutinefunction(method):
+        if inspect.iscoroutinefunction(method):
             wrapped = functools.update_wrapper(async_wrapper, method)
         else:
             wrapped = functools.update_wrapper(wrapper, method)