Sync two-bucket

[mk-mxp]

Two tests were added to canonical data. They look like there is no need to re-run tests.

I also removed an unused private field and folded the one-line DocBlocks to my prefered style.

[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.

[no important files changed]

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