Skip test on macOS 12.6

* tests/xform04.at: Skip test on macOS 12.6, which is behind the times
and doesn’t think that ⱥ (U+2C65 LATIN SMALL LETTER A WITH STROKE) is
printable.

tests/xform04.at

@@ -39,6 +39,8 @@ if test "`(locale charmap) 2>/dev/null`" != UTF-8; then
   done
 fi
 
+expr Aa.Ⱥⱥ : 'Aa\.[[:print:]][[:print:]]$' >/dev/null || AT_SKIP_TEST
+
 genfile --file Aa.Ⱥⱥ
 tar -cvf /dev/null --transform='s/.*/\L&-\U&/' --show-transformed-name Aa.Ⱥⱥ],
 [0],