Improve behaviour when adding name.md files in batches and encountering duplicates

[stefaniebutland]

3. GitHub Clinic - Generate Markdown Files for Each Participant

when running

## create .md files for each Champion
kyber::[short_names](https://openscapes.github.io/kyber/reference/short_names.html)(cohort$first, cohort$last) |>
   [create_github_clinic](https://openscapes.github.io/kyber/reference/create_github_clinic.html)(here())

Encountered error when I create .md files for each Champion in batches e.g. 3 cohorts + mentors (> 150 in total). When kyber::short_names encounters a name.md file that already exists, it stops and does not add remaining files in the tibble. Ideally it would go through full tibble and error msg would indicate which individual name.md already existed