gh-102251: Fix reference leak in _testsinglephase initialization (#105082)

Correctly decref 'initialized' in init_module()

Co-authored-by: Erlend E. Aasland <[email protected]>

Author: sunmy2019

Modules/_testsinglephase.c

@@ -140,7 +140,9 @@ init_module(PyObject *module, module_state *state)
     if (initialized == NULL) {
         return -1;
     }
-    if (PyModule_AddObjectRef(module, "_module_initialized", initialized) != 0) {
+    int rc = PyModule_AddObjectRef(module, "_module_initialized", initialized);
+    Py_DECREF(initialized);
+    if (rc < 0) {
         return -1;
     }