feat: add negative midnight test case for clock exercise

[Qubi0-0]

The test did not include situations where the final hours are equal to -24 and the minutes are equal to 0. This situation should also return 00:00. I added the test case {-24, 0, "00:00", "negative midnight is zero hours"} to ensure this is now checked. Both 24:00 and -24:00 should return the same result.

[github-actions]

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