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