Fix unused exitcode in macos export plugin

Fix that the exitcode is never set.

platform/macos/export/export_plugin.cpp

@@ -727,7 +727,7 @@ Error EditorExportPlatformMacOS::_code_sign(const Ref<EditorExportPreset> &p_pre
 			String str;
 			int exitcode = 0;
 
-			Error err = OS::get_singleton()->execute("codesign", args, &str, nullptr, true);
+			Error err = OS::get_singleton()->execute("codesign", args, &str, &exitcode, true);
 			if (err != OK) {
 				add_message(EXPORT_MESSAGE_WARNING, TTR("Code Signing"), TTR("Could not start codesign executable, make sure Xcode command line tools are installed."));
 				return err;