spec: fix pseudonym_sessions_controller_spec.rb

Change-Id: Ia2957d25192d194cc9be45032068bc243469e991
Reviewed-on: https://gerrit.instructure.com/38775
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
Product-Review: Jon Jensen <jon@instructure.com>
QA-Review: Jon Jensen <jon@instructure.com>