todaysFactsWidget: Fix broken layout in GNOME 45

Using St.ScrollView.add_child() instead of St.ScrollView.add_actor()
leads to broken layout in the ScrollView widget (zero vertical extension
of rows). See
#362 (comment)
and follow-up comments.

But unlike other St Widgets, ScrollView still supports the add_actor() method
in GNOME 46. So keep using it.

extension/widgets/todaysFactsWidget.js

@@ -48,7 +48,7 @@ class TodaysFactsWidget extends St.ScrollView {
             reactive: true
         });
         this.factsBox.add_child(this.facts_widget);
-        this.add_child(this.factsBox);
+        this.add_actor(this.factsBox);
 
     }