bpo-38631: Add _Py_NO_RETURN to functions calling Py_FatalError() (GH-18278)

Add _Py_NO_RETURN to functions calling Py_FatalError():

* _PyObject_AssertFailed()
* dummy_dealloc()
* faulthandler_fatal_error_thread()
* none_dealloc()
* notimplemented_dealloc()
diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index 75e5599..dc8fd6f 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -443,7 +443,7 @@
    NDEBUG against a Python built with NDEBUG defined.
 
    msg, expr and function can be NULL. */
-PyAPI_FUNC(void) _PyObject_AssertFailed(
+PyAPI_FUNC(void) _Py_NO_RETURN _PyObject_AssertFailed(
     PyObject *obj,
     const char *expr,
     const char *msg,