Fixed the issue that prevented users from retrying to send the form

The issue raises when user retries to send the registration form after any validation error, only when registering an A/B test and, at the same time, seems to be related to the value that the Values field had before and after the retry.

I think the scenarios we should try are the following:

• Try to register an A/B test with no value for the Values field for the Feature variant and, after seeing the validation error, try again filling properly all the fields
• Try to register an A/B test with value for the Values field for the Feature variant but no value for any other field (to make validation fails). After seeing the validation error, try again filling properly all the fields

Closes T378022