Add canonical tests to `list-ops`

[BNAndras]

Closes #418 by removing the offending tests and adding the canonical tests from the problem-specs repo.

This will break existing solutions because previously students implemented my-fold but now we're asking for my-foldl and my-foldr instead.

[github-actions[bot]]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

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[BNAndras]

@exercism/racket