docs: set_allow_multiselect is now correctly documented

[Jaskowicz1]

This PR corrects the documentation for set_allow_multiselect as it had the same documentation as set_duration.

Code change checklist

• [x] I have ensured that all methods and functions are fully documented using doxygen style comments.
• [x] My code follows the coding style guide.
• [x] I tested that my change works before raising the PR.
• [x] I have ensured that I did not break any existing API calls.
• [x] I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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