Rails implemented a CSRF token storage strategy to allow storing the
CSRF tokens outside of the sessios (for example, in an encrypted
cookie), and changed how the value is kept around during the request
cycle, by using a request.env value.
We still want to ensure the final session value is cleaned correctly in
the test, but the implementation needed to change since we can't simply
delete from the session anymore, we need to make sure we call the Rails
methods for resetting the current storage strategy so it works with all
of them.
https://github.com/rails/rails/pull/44283
b5172a0cdb