Add test for controlling height between states
Add test for controlling height between states

The button shouldn't change its vertical position
when the state changes. The text confirming the
copy is just one line so setting height for both
based on the API key, which can run to 2 lines
makes sense.

Explained in this PR:

https://github.com/alphagov/notifications-admin/pull/2428

alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin