[3.13] gh-130163: Fix a leak in _pickle.c after backporting (GH-130568)

Author: serhiy-storchaka

Modules/_pickle.c

@@ -1938,39 +1938,46 @@ whichmodule(PyObject *global, PyObject *dotted_path)
         i = 0;
         while (PyDict_Next(modules, &i, &module_name, &module)) {
             if (_checkmodule(module_name, module, global, dotted_path) == 0) {
+                Py_DECREF(modules);
                 return Py_NewRef(module_name);
             }
             if (PyErr_Occurred()) {
+                Py_DECREF(modules);
                 return NULL;
             }
         }
     }
     else {
         PyObject *iterator = PyObject_GetIter(modules);
         if (iterator == NULL) {
+            Py_DECREF(modules);
             return NULL;
         }
         while ((module_name = PyIter_Next(iterator))) {
             module = PyObject_GetItem(modules, module_name);
             if (module == NULL) {
                 Py_DECREF(module_name);
                 Py_DECREF(iterator);
+                Py_DECREF(modules);
                 return NULL;
             }
             if (_checkmodule(module_name, module, global, dotted_path) == 0) {
                 Py_DECREF(module);
                 Py_DECREF(iterator);
+                Py_DECREF(modules);
                 return module_name;
             }
             Py_DECREF(module);
             Py_DECREF(module_name);
             if (PyErr_Occurred()) {
                 Py_DECREF(iterator);
+                Py_DECREF(modules);
                 return NULL;
             }
         }
         Py_DECREF(iterator);
     }
+    Py_DECREF(modules);
 
     /* If no module is found, use __main__. */
     return &_Py_ID(__main__);