FIX: Allow sanitized-HTML in GH issues and categories oneboxes. (#25374)

Follow-up to d78357917c

Related meta topic: https://meta.discourse.org/t/html-is-not-render-on-category-onebox-description/289424:

lib/onebox/engine/github_issue_onebox.rb

@@ -40,7 +40,10 @@ module Onebox
         body, excerpt = compute_body(raw["body"])
         ulink = URI(link)
 
-        labels = raw["labels"].map { |l| { name: Emoji.codes_to_img(CGI.escapeHTML(l["name"])) } }
+        labels =
+          raw["labels"].map do |l|
+            { name: Emoji.codes_to_img(Onebox::Helpers.sanitize(l["name"])) }
+          end
 
         {
           link: @url,