[REV] web_editor: revert summernote update

Summernote was updated alongside the new editor of saas-12.2. However,
since we are putting back the editor of 12.0, summernote needs to be
downgraded back to the version that was compatible with the 12.0 editor.

This is a revert of 17c6d005.

Part of PR 35677.

Co-authored-by: Nicolas Bayet <nby@odoo.com>
Co-authored-by: Antoine Guenet <age@odoo.com>
Co-authored-by: Christophe Matthieu <chm@odoo.com>
Co-authored-by: David Monjoie <dmo@odoo.com>