GtkBuilder uses GMarkup, which defines a boolean attribute value as:
- yes/no
- true/false
- 1/0
The ITS file for GtkBuilder UI definitions is only using the first pair,
likely because Glade only ever used those values. GTK's own tools, though,
will typically simplify the full yes/no and true/false strings to 1 and 0,
to minimise the parsing time.
Fixes: #4596