tests: stty.sh: skip on systems without perl

* init.cfg (stty_reversible_init_): Add require_perl_
to ensure we skip rather than error, without perl.

init.cfg

@@ -384,6 +384,7 @@ rwx_to_mode_()
 # with a space.
 stty_reversible_init_()
 {
+  require_perl_
   # Pad start with one space for the first option to match in query function.
   stty_reversible_=' '$(perl -lne '/^ *{"(.*?)",.*\bREV\b/ and print $1' \
     "$abs_top_srcdir"/src/stty.c | tr '\n' ' ')