gh-84753: Make inspect.iscoroutinefunction() work with AsyncMock (GH-94050) (GH-94461)

The inspect version was not working with unittest.mock.AsyncMock.

The fix introduces special-casing of AsyncMock in
`inspect.iscoroutinefunction` equivalent to the one
performed in `asyncio.iscoroutinefunction`.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
(cherry picked from commit 4261b6bffc)

Co-authored-by: Mehdi ABAAKOUK <sileht@sileht.net>

Lib/test/test_asyncio/test_tasks.py

@@ -1723,6 +1723,7 @@ def fn2():
         self.assertTrue(asyncio.iscoroutinefunction(fn2))
 
         self.assertFalse(asyncio.iscoroutinefunction(mock.Mock()))
+        self.assertTrue(asyncio.iscoroutinefunction(mock.AsyncMock()))
 
     def test_yield_vs_yield_from(self):
         fut = self.new_future(self.loop)