docs: Escape tags in GtkBuilder description
Fixes the tags and the rest of the gi-docgen created HTML page not being visible in a browser.
See: https://gnome.pages.gitlab.gnome.org/gtk/gtk4/class.Builder.html#a-gtkbuilder-ui-definition
Fixes the tags and the rest of the gi-docgen created HTML page not being visible in a browser.
See: https://gnome.pages.gitlab.gnome.org/gtk/gtk4/class.Builder.html#a-gtkbuilder-ui-definition