[web/test] stop calling loadxhtml with a form.callback It was deprecated in 3.9 (changeset 7b9553a9db65) and removed in 3.18. Related to #5533303.

include *.py
include */*.py
recursive-include data *.gif *.png *.ico *.css *.js
recursive-include i18n *.po
recursive-include wdoc *