GH-89091: raise RuntimeWarning for unawaited async generator methods (#104611)

Python/_warnings.c

@@ -1365,6 +1365,20 @@ exit:
     return ret;
 }
 
+void
+_PyErr_WarnUnawaitedAgenMethod(PyAsyncGenObject *agen, PyObject *method)
+{
+    PyObject *exc = PyErr_GetRaisedException();
+    if (_PyErr_WarnFormat((PyObject *)agen, PyExc_RuntimeWarning, 1,
+                          "coroutine method %R of %R was never awaited",
+                          method, agen->ag_qualname) < 0)
+    {
+        PyErr_WriteUnraisable((PyObject *)agen);
+    }
+    PyErr_SetRaisedException(exc);
+}
+
+
 void
 _PyErr_WarnUnawaitedCoroutine(PyObject *coro)
 {