devel/schilybase: work around bug in gettext-0.22

gettext 0.22 started to transcode PO files to UTF-8 before processing
them, converting all msgids and messages to Unicode in the process.
This breaks schilytools which assumes msgids are in ISO-8859-1 encoding.
Work around the breakage using the new --no-convert option. A bug
report was filed with upstream in the hope that they may fix the bug.

Reported by: bugzeo <kiboto6933@eyeremind.com>
See also: https://savannah.gnu.org/news/?id=10378
PR: 257905
MFH: 2023Q4

(cherry picked from commit e8c2558f623d87d044e0dec460f606a40a46d359)