tests: Skip when zsh/pcre is not available

highlighters/regexp/test-data/word-boundary.zsh

@@ -27,6 +27,7 @@
 # vim: ft=zsh sw=2 ts=2 et
 # -------------------------------------------------------------------------------------------------
 
+if zmodload -s zsh/pcre; then
   setopt RE_MATCH_PCRE
 
   ZSH_HIGHLIGHT_REGEXP+=('\bsudo\b' 'fg=white,bold,bg=red')
@@ -36,3 +37,6 @@ BUFFER='sudo ls'
   expected_region_highlight=(
     "1 4 fg=white,bold,bg=red"
   )
+else
+  skip_test='Test requires zsh/pcre'
+fi