bird-watcher: Add test case for a week in the end of the log

[mugane-dj]

The test cases provided in the exercise for the BirdsInWeek function only cover the first week and a week in the middle of the log. An edge case for a week in the end of the log is missing.

[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.

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[no important files changed]

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[github-actions]

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[andrerfcsantos]

Thanks for this!