gh-118926: Spill deferred references to stack in cases generator (#122748)

This automatically spills the results from `_PyStackRef_FromPyObjectNew`
to the in-memory stack so that the deferred references are visible to
the GC before we make any possibly escaping call.

Co-authored-by: Ken Jin <[email protected]>

Author: colesbury

Python/bytecodes.c

@@ -1424,7 +1424,7 @@ dummy_func(
                                  "no locals found");
                 ERROR_IF(true, error);
             }
-            locals = PyStackRef_FromPyObjectNew(l);;
+            locals = PyStackRef_FromPyObjectNew(l);
         }
 
         inst(LOAD_FROM_DICT_OR_GLOBALS, (mod_or_class_dict -- v)) {