DEV: Future-proof htmlSafe interactions (#23596)

See https://github.com/discourse/discourse-encrypt/pull/282

> `cooked` was an Ember SafeString. The internal storage of the string changed from `.string` to `.__string` at some point between Ember 3.28 and Ember 5. Instead, we can use `toString()` which is guaranteed to work in all situations

plugins/styleguide/assets/javascripts/discourse/components/styleguide-markdown.js

@@ -6,6 +6,8 @@ export default Component.extend({
     this._super(...arguments);
 
     const contents = $(this.element).html();
-    cookAsync(contents).then((cooked) => $(this.element).html(cooked.string));
+    cookAsync(contents).then((cooked) =>
+      $(this.element).html(cooked.toString())
+    );
   },
 });