QmlDesigner: Silence more warnings

Change-Id: I8982ce6fe2860950e92b95e1bf02d22e857939d7
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qmldesigner/designercore/projectstorage/modulescanner.h

@@ -33,9 +33,9 @@ private:
     void scan(std::string_view modulePaths);
 
 private:
-    SkipFunction m_skip;
+    [[maybe_unused]] SkipFunction m_skip;
     Imports m_modules;
-    VersionScanning m_versionScanning;
+    [[maybe_unused]] VersionScanning m_versionScanning;
 };
 
 } // namespace QmlDesigner