fix(git): git_status_prompt must respects spaces to properly match prefixes

`git_status_prompt` was always empty as whitespace around the keys for `$prefix_constant_map` were trimmed. The in list of the for loop must be enclosed in `"` to avoid trimming, which in return requires the iterator specifier to contain an `@` to avoid concatenation of all keys. This is important for the regex to work properly.

lib/git.zsh

@@ -117,7 +117,7 @@ function _omz_git_prompt_status() {
   fi
 
   # For each status prefix, do a regex comparison
-  for status_prefix in ${(k)prefix_constant_map}; do
+  for status_prefix in "${(@k)prefix_constant_map}"; do
     local status_constant="${prefix_constant_map[$status_prefix]}"
     local status_regex=$'(^|\n)'"$status_prefix"