Use proper format specifier for size_t value in ipc sample

"%d" can't be used for size_t which may be of greater size than int, so use
"%lu" with a cast to unsigned long, as is done elsewhere because "%z" is
unfortunately not portable.

Closes #17255.

samples/ipc/connection.h

@@ -69,7 +69,7 @@ protected:
               break;
         }
 
-        wxLogMessage("%s,%d)", s, size);
+        wxLogMessage("%s,%lu)", s, (unsigned long)size);
     }
 };