Issue #24268: Address some PEP 489 refleaks

- missing DECREF in PyModule_FromDefAndSpec2
- missing DECREF in PyType_FromSpecAndBases2
- missing DECREF in _testmultiphase module

Patch by Petr Viktorin
diff --git a/Objects/moduleobject.c b/Objects/moduleobject.c
index 7a86a5b..7b41b0b 100644
--- a/Objects/moduleobject.c
+++ b/Objects/moduleobject.c
@@ -311,6 +311,7 @@
         }
     }
 
+    Py_DECREF(nameobj);
     return m;
 
 error: