LibGUI: Invalidate GroupBox layout on font change

Author: https://github.com/frhun
Commit: a21ea5f10f
Pull-request: https://github.com/SerenityOS/serenity/pull/10246
Issue: https://github.com/SerenityOS/serenity/issues/5887
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibGUI/GroupBox.h

@@ -23,6 +23,7 @@ protected:
     explicit GroupBox(const StringView& title = {});
 
     virtual void paint_event(PaintEvent&) override;
+    virtual void fonts_change_event(FontsChangeEvent&) override;
 
 private:
     String m_title;