Stop using json shema gem in test [RUN AS-IF-FOSS]

What does this MR do?

We switched to using json-schemer gem in production. !56745 (merged)

We couldn't use json-schema in tests because it needed a bigger change, this MR is a follow-up for that

Does this MR meet the acceptance criteria?

Tests are passing

Related issue

#325727 (closed)

Conformity

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  • I have not included a changelog entry because previous MR has changelog that encapsulates the change.

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