textproc/itstool: Update to 2.0.6, Add patch to fix some libxml issues [1]

FreeBSD Doc translations are working fine with this patch.
More details on https://github.com/itstool/itstool/issues/38

PR: 244325
Approved by: maintainer timeout (kwm, > 3 weeks)
Obtained from: https://github.com/itstool/itstool/pull/18 [1]