[gtk] (2 commits) ...Merge branch 'fix_cast_warning_adding_notebook_page' into 'master'

From: Matthias Clasen <matthiasc src gnome org>
To: commits-list gnome org
Cc:
Subject: [gtk] (2 commits) ...Merge branch 'fix_cast_warning_adding_notebook_page' into 'master'
Date: Tue, 1 Jun 2021 16:18:32 +0000 (UTC)

Summary of changes:

  9c79b8b... invalid cast from 'GtkButton' to 'GtkBox'
  7d3c3cb... Merge branch 'fix_cast_warning_adding_notebook_page' into '