LibGfx+LibWeb: Store Typeface and Font-related types in RefPtr to const

Author: https://github.com/ADKaster
Commit: be2dd91289
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4362
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/Hendiadyoin1

Libraries/LibWeb/Painting/MediaPaintable.h

@@ -31,7 +31,7 @@ private:
         DevicePixelRect timeline_rect;
 
         String timestamp;
-        RefPtr<Gfx::Font> timestamp_font;
+        RefPtr<Gfx::Font const> timestamp_font;
         DevicePixelRect timestamp_rect;
 
         DevicePixelRect speaker_button_rect;