[3.15] gh-159739: Avoid leaking references during free-threaded GC enumeration (GH-159781) (#159907)

(cherry picked from commit 7652a6d)

Co-authored-by: Jelle Zijlstra <jelle@openai.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Author: 3 people

Misc/NEWS.d/next/Core_and_Builtins/2026-10-19-20-38-17.gh-issue-159739.55fd08.rst

@@ -0,0 +1,2 @@
+Fix a reference leak in :func:`gc.get_objects` and :func:`gc.get_referrers`
+when an internal allocation fails in the free-threaded build.

Python/gc_free_threading.c

@@ -2389,9 +2389,10 @@ visit_get_referrers(const mi_heap_t *heap, const mi_heap_area_t *area,
         return true;
     }
     if (Py_TYPE(op)->tp_traverse(op, referrersvisit, arg->objs)) {
-        if (_PyObjectStack_Push(&arg->results, Py_NewRef(op)) < 0) {
+        if (_PyObjectStack_Push(&arg->results, op) < 0) {
             return false;
         }
+        Py_INCREF(op);
     }
 
     return true;
@@ -2436,9 +2437,10 @@ visit_get_objects(const mi_heap_t *heap, const mi_heap_area_t *area,
     }
 
     struct get_objects_args *arg = (struct get_objects_args *)args;
-    if (_PyObjectStack_Push(&arg->objects, Py_NewRef(op)) < 0) {
+    if (_PyObjectStack_Push(&arg->objects, op) < 0) {
         return false;
     }
+    Py_INCREF(op);
     return true;
 }