fix: Added Skip to the Fact attribute

[DerSimeon]

The Title says it all. All Tests in the csharp track except this one have the Skip Attribute on each test except the first one. This Exercise was left out.

[github-actions]

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[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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[ErikSchierboom]

This is a refactoring exercise and the stub implementation should therefore pass all the tests from the start. There is no need for TDD.