Unable to change Premium version

[jcomack]

Please give us a description of what happened.

While attempting to write some test instructions for Yoast SEO Premium, including a step that involves using Yoast Test helper, I noticed that when Premium is activated, the version number isn't displayed in its proper field. It seems that changing Premium's version also doesn't change anything, despite the confirmation showing up on screen, but I'm not able to properly verify this.

Please describe what you expected to happen and why.

I expected the version of Premium, being present in the Premium field and to also be updated.

How can we reproduce this behavior?

1. Enable both Yoast Test helper and Yoast SEO Premium (15.6, for example)
2. Navigate to Tools -> Yoast Test
3. See that the Yoast SEO Premium field is empty, and the Yoast SEO field is not
4. Change the version number in the Yoast SEO Premium field (14.0, for example) and click Save
5. See that the field remains empty, despite receiving the notification that the option was successfully updated.