Fix redirects to issue sidebar JSON after sign in

What does this MR do?

This fixes a bug where users were being redirected to the issue sidebar JSON when visiting /users/sign_in

Steps to Reproduce

1. Open an issue.
2. Find the xxx.json?serializer=sidebar_extras request in the inspector and resend the request. (To make sure this AJAX request finishes after the HTML request for the issue and the session here is the last one written to Redis)
3. Visit /users/sign_in.

Does this MR meet the acceptance criteria?

Conformity

• 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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #267583 (closed)