calls-application: Stop using GdkScreen

https://docs.gtk.org/gtk4/migrating-3to4.html#adapt-to-gtkwidgets-size-allocation-changes

Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/714>

src/calls-application.c

@@ -510,7 +510,7 @@ startup (GApplication *application)
 
   provider = gtk_css_provider_new ();
   gtk_css_provider_load_from_resource (provider, "/org/gnome/Calls/style.css");
-  gtk_style_context_add_provider_for_screen (gdk_screen_get_default (),
+  gtk_style_context_add_provider_for_display (gdk_display_get_default (),
                                               GTK_STYLE_PROVIDER (provider),
                                               GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
 }