Fix #7189: autodoc: classmethod coroutines are not detected

tests/roots/test-ext-autodoc/target/coroutine.py

@@ -3,6 +3,16 @@ class AsyncClass:
         """A documented coroutine function"""
         attr_coro_result = await _other_coro_func()  # NOQA
 
+    @classmethod
+    async def do_coroutine2(cls):
+        """A documented coroutine classmethod"""
+        pass
+
+    @staticmethod
+    async def do_coroutine3():
+        """A documented coroutine staticmethod"""
+        pass
+
 
 async def _other_coro_func():
     return "run"