Fix unit tests for the Plus Expiration page

[Vinnl]

In #5994 and #5988 , we disabled the unit tests for the Plus Expiration page because they failed every now and then without the code actually being broken (or even having changed at all). We should find out what makes the tests flaky, and fix that.

Acceptance criteria:

• There are no .skip calls in the PlusExpiration tests anymore
• There are no c8 ignore statements in the PlusExpiration code
• The tests succeed predictably

(Internal ticket: MNTOR-4686)