Sync and add reverse-string tests

[codingthat]

No description provided.

[github-actions]

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.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

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[codingthat]

(Sorry, missed that detail earlier.)

[codingthat]

Probably a good candidate to add a hints.md given the trick needed to pass the new tests.

[meatball133]

You can't see hints in the web editor for practice exercises, so I think it is better to put them in an instruction append doc if needed.

[codingthat]

Done, thanks!