Switch from respond_with_navigational to redirect_to

This replaces respond_with_navigational with redirect_to when redirecting to the sign-in form after a failed sign-in attempts.

There seems to be an issue with respond_with_navigational that prevents feature flags and other properties like the ArkoseLabs public key from being pushed to the frontend. This issue does not seem to happen when using redirect_to.

Changelog: fixed

How to reproduce this?

1. Checkout the master branch.
2. Enable the echo arkose_labs_login_challenge feature flag:

   echo "Feature.enable(:arkose_labs_login_challenge)" | rails c

3. Expose the ARKOSE_LABS_PUBLIC_KEY and restart the GDK in the same terminal:

   export ARKOSE_LABS_PUBLIC_KEY="9F5BDFCD-E895-43B5-8D96-B24E0107B685"
   gdk restart

4. Apply the following patch to force the ArkoseLabs token verification to fail:

   diff --git a/ee/app/services/arkose/user_verification_service.rb b/ee/app/services/arkose/user_verification_service.rb
   index 7aa9d540844..1b4aaddd25e 100644
   --- a/ee/app/services/arkose/user_verification_service.rb
   +++ b/ee/app/services/arkose/user_verification_service.rb
   @@ -12,6 +12,7 @@ def initialize(session_token:, user:)
        end
    
        def execute
   +      return false
          response = Gitlab::HTTP.perform_request(Net::HTTP::Post, VERIFY_URL, body: body).parsed_response
          logger.info(build_message(response))
    

5. Sign-out of your running GDK instance.
6. Try to sign-in with valid credential.
   • You should see the Login failed. Please retry from your primary device and network. error.
   • In the browser's console, you should see the following error: index.js?fec1:3 Uncaught TypeError: Cannot read properties of undefined (reading 'arkoseLabsLoginChallenge')
   • Executing gon.features in the brower's console returns undefined.
7. Checkout this branch and repeat steps 4 to 6.
   • You should still see the Login failed. Please retry from your primary device and network. error.
   • In the console, there should be no uncaught TypeError.
   • You should see the enabled feature flags when executing gon.features in the console.