Fixing request json mime type

What does this MR do?

Fixes a problem with the request mime type when any of the User and IP Rate Limits are enabled.

Why was this MR needed?

When one of this options is enabled and we try to request a json the response was wrong because the mime type set in the request was invalid.

The origin of problem the problem is this:

• One of the Rack::Attack throttle blocks is run. Inside it, there is a call to Gitlab::Auth::RequestAuthenticator.new(self).user&.id.
• The find_user_from_rss_token in Gitlab::Auth::UserAuthFinders is called by the user method of Gitlab::Auth::RequestAuthenticator.
• The guard clause of this method says:

return unless current_request.path.ends_with?('.atom') || current_request.format.atom?

Here is the root of the problem. The call to the current_request.format.

Right now, the current_request.env['action_dispatch.request.formats'] is nil. But the call to the format method without any relevant param makes actionpack to choose the first mime type available, which is */*. And therefore, that value is memoized and set in the request. That's why, when the request reaches the controller, despite of having the parameter format to json it serves the HTML version of the page.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #41598 (closed)