fix CTA text logic

[gumaerc]

What are the relevant tickets?

Closes https://github.com/mitodl/hq/issues/9101

Description (What does it do?)

This PR fixes the logic controlling the text of the CTA on dashboard card buttons. "View" is now used as the verb in cases where the end date of the course has passed or the enrollment status is "completed."

How can this be tested?

• Make sure you have a locally running instance of MITx Online and have set it up to be run on the same Keycloak / APISIX instance as Learn, as described in the Learn README
• Spin up mit-learn on this branch, linked to your instance of MITx Online
• Make sure you are enrolled in multiple courses, either through a B2B organization / contract or personal enrollments on your test account
• Make sure one of the enrollments is marked as completed
• Log in to the Learn dashboard and view your enrollments
• Verify that the completed enrollment shows a button that says "View" and the uncompleted one says "Continue"

[jonkafton]

👍

Would be good to add a test to cover enrollmentStatus not completed and end date in past -> "View Course".