Use consistent bash5 style for conditionals and quoting

bin/omarchy-theme-set

@@ -12,7 +12,7 @@ OMARCHY_THEMES_PATH="$OMARCHY_PATH/themes"
 
 THEME_NAME=$(echo "$1" | sed -E 's/<[^>]+>//g' | tr '[:upper:]' '[:lower:]' | tr ' ' '-')
 
-if [[ ! -d "$OMARCHY_THEMES_PATH/$THEME_NAME" ]] && [[ ! -d "$USER_THEMES_PATH/$THEME_NAME" ]]; then
+if [[ ! -d $OMARCHY_THEMES_PATH/$THEME_NAME ]] && [[ ! -d $USER_THEMES_PATH/$THEME_NAME ]]; then
   echo "Theme '$THEME_NAME' does not exist"
   exit 1
 fi