general: Use gtk_widget_set_visible

A lot of places were using gtk_widget_show/gtk_widget_hide, but those
methods are deprecated since Gtk 4.10.

Let's use gtk_widget_set_visible instead.

src/gui/calendar-management/gcal-calendar-management-dialog.c

@@ -144,7 +144,7 @@ setup_context (GcalCalendarManagementDialog *self)
       page = g_object_new (pages[i].gtype,
                            "context", self->context,
                            NULL);
-      gtk_widget_show (GTK_WIDGET (page));
+      gtk_widget_set_visible (GTK_WIDGET (page), TRUE);
 
       gtk_stack_add_titled (GTK_STACK (self->stack),
                             GTK_WIDGET (page),

src/gui/calendar-management/gcal-file-chooser-button.c

@@ -75,7 +75,7 @@ on_filechooser_dialog_response_cb (GtkFileChooser        *filechooser,
       gcal_file_chooser_button_set_file (self, file);
     }
 
-  gtk_widget_hide (GTK_WIDGET (filechooser));
+  gtk_widget_set_visible (GTK_WIDGET (filechooser), FALSE);
 }
 static void
 ensure_filechooser (GcalFileChooserButton *self)