DEV: Minor hashtag to-markdown fix (#19142)

Follow-up to 3846b6248f,
check if class contains hashtag-cooked rather than
it being the only class.

app/assets/javascripts/discourse/app/lib/to-markdown.js

@@ -315,7 +315,7 @@ export class Tag {
           return text;
         }
 
-        if ("hashtag-cooked" === attr.class) {
+        if (attr.class?.includes("hashtag-cooked")) {
           if (attr["data-ref"]) {
             return `#${attr["data-ref"]}`;
           } else {