gh-132775: Fix Recently Introduced Warnings

Modules/_interpchannelsmodule.c

@@ -3443,7 +3443,7 @@ channelsmod_get_channel_defaults(PyObject *self, PyObject *args, PyObject *kwds)
     }
     int64_t cid = cid_data.cid;
 
-    struct _channeldefaults defaults;
+    struct _channeldefaults defaults = {0};
     int err = channel_get_defaults(&_globals.channels, cid, &defaults);
     if (handle_channel_error(err, self, cid)) {
         return NULL;

Modules/_interpqueuesmodule.c

@@ -1772,7 +1772,7 @@ queuesmod_get_queue_defaults(PyObject *self, PyObject *args, PyObject *kwds)
     }
     int64_t qid = qidarg.id;
 
-    struct _queuedefaults defaults;
+    struct _queuedefaults defaults = {0};
     int err = queue_get_defaults(&_globals.queues, qid, &defaults);
     if (handle_queue_error(err, self, qid)) {
         return NULL;

Python/crossinterp.c

@@ -1795,6 +1795,7 @@ typedef struct _sharednsitem {
     // in a different interpreter to release the XI data.
 } _PyXI_namespace_item;
 
+#ifndef NDEBUG
 static int
 _sharednsitem_is_initialized(_PyXI_namespace_item *item)
 {
@@ -1803,6 +1804,7 @@ _sharednsitem_is_initialized(_PyXI_namespace_item *item)
     }
     return 0;
 }
+#endif
 
 static int
 _sharednsitem_init(_PyXI_namespace_item *item, PyObject *key)