[3.10] gh-84753: Make inspect.iscoroutinefunction() work with AsyncMock (GH-94050)

[miss-islington]

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 4261b6b)

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

• Issue: inspect.iscorutinefunction() returns False for unittest.mock.AsyncMock instances #84753