tests: Directly diff expected_region_highlight against region_highlight

highlighters/main/test-data/parameter-star.zsh

@@ -32,5 +32,9 @@ BUFFER='() { : $* }'
 # This tests that $* isn't highlighted as a glob.
 # If we ever add a "unquoted parameter" style, the expectation may change.
 expected_region_highlight=(
+  "1 2 reserved-word" # ()
+  "4 4 reserved-word" # {
+  "6 6 builtin" # :
   "8 9 default" # $*
+  "11 11 reserved-word" # }
 )