tests: Followup to fd061b5730bf: quote both expected and actual output.

tests/test-highlighting.zsh

@@ -110,7 +110,7 @@ run_test_internal() {
     [[ -n "$highlight_zone[4]" ]] && todo=" # TODO $highlight_zone[4]"
     for j in {$highlight_zone[1]..$highlight_zone[2]}; do
       if [[ "$observed_result[$j]" != "$highlight_zone[3]" ]]; then
-        echo "not ok $i ${(qqq)BUFFER[$highlight_zone[1],$highlight_zone[2]]} [$highlight_zone[1],$highlight_zone[2]]: expected $highlight_zone[3], observed ${(qqq)observed_result[$j]}.$todo"
+        echo "not ok $i ${(qqq)BUFFER[$highlight_zone[1],$highlight_zone[2]]} [$highlight_zone[1],$highlight_zone[2]]: expected ${(qqq)highlight_zone[3]}, observed ${(qqq)observed_result[$j]}.$todo"
         continue 2
       fi
     done