Cleanup shellcheck warnings (#178)

* chore: shellcheck-warnings for catppuccin.tmux

Command used: `shellcheck catppuccin.tmux -ax -s bash`

* shellcheck: fix all warnings

Command used: `shellcheck -a catppuccin.tmux $(ls custom/*.sh pane/*.sh status/*.sh window/*.sh)`

* shellcheck: update workflow to check warnings

* shellcheck: include warnings from sourced files

utils/module_utils.sh

@@ -16,7 +16,7 @@ load_modules() {
     # extract the substring from start of string up to delimiter.
     iter=${IN%% *}
     # delete this first "element" AND next separator, from $IN.
-    IN="${IN#$iter }"
+    IN="${IN#"$iter "}"
     # Print (or doing anything with) the first "element".
 
     module_name=$iter
@@ -25,6 +25,7 @@ load_modules() {
       module_path="$module_dir/$module_name.sh"
 
       if [ -r "$module_path" ]; then
+        # shellcheck source=/dev/null
         source "$module_path"
         loaded_modules="$loaded_modules$( "show_$module_name" "$module_index" )"
         module_index+=1