transpose: rename function to transposition

[keiravillekode]

Previously, a student could submit an empty file as the solution file and the tests would pass, as 'transpose' is a built-in function.

https://discord.com/channels/854117591135027261/1482397144580227232/1482397799319474310

[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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[keiravillekode]

The reverse-string exercise has the same issue.

https://discord.com/channels/854117591135027261/1482397144580227232/1482642215745359986

We could rename that exercise function to reversal