Fix "sign out" button in error pages

What does this MR do?

This MR fixes #322980 (closed) by adding the missing JavaScript. We are guessing this was broken when we refactored the Rails JS into rails_ujs.

Thanks @leipert & @cwoolley-gitlab for pairing https://youtu.be/cEoLQNq7p_U!

Screenshots (strongly suggested)

404 Page	After click "Sign out..."

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #322980 (closed)