This can be used to set a custom text for the license if it can't be set via property@AboutDialog:license-type.
When set, property@AboutDialog:license-type will be set to [gtk.types.License.Custom].
The license text will be displayed on the Legal page, below the copyright information.
License text can contain Pango markup and links.
[adw.about_dialog.AboutDialog.addLegalSection] can be used to add license information for the application dependencies or other components.