Fix GCC 13 warning about freeing the global static

I believe the problem is that QGlobalStatic::operator Type *() may
return a null pointer, in which case the compiler is right that we could
attempt to free the shared_null. Instead use QGlobalStatic::operator*,
which doesn't ever return nullptr.

Change-Id: I9201d9ecf52f4146bb04fffd17644782bf0eb9d1
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/printsupport/kernel/qprinterinfo.cpp

@@ -21,7 +21,7 @@ class QPrinterInfoPrivateDeleter
 public:
     static inline void cleanup(QPrinterInfoPrivate *d)
     {
-        if (d != shared_null)
+        if (d != &*shared_null)
             delete d;
     }
 };