Merge pull request #37134 from rmacklin/fix-code-block-in-rails-guides-generated-html

Fix code block in the HTML version of the upgrade guide

[ci skip]

guides/source/upgrading_ruby_on_rails.md

@@ -116,6 +116,7 @@ to be able to rollback set
 If you were previously loading any of the `actioncable`, `activestorage`,
 or `rails-ujs` packages through npm/yarn, you must update the names of these
 dependencies before you can upgrade them to `6.0.0`:
+
 ```
 actioncable   → @rails/actioncable
 activestorage → @rails/activestorage