Fix `Build and Deploy` workflow

After merging #455, the Build and Deploy workflow fails, see: https://github.com/carpentries-incubator/deep-learning-intro/actions/runs/8881072163/job/24382959500

[...]
── Creating Images page ────────────────────────────────────────────────────────
  Writing ''instructor/images.html''
  Writing ''images.html''
── Creating Instructor Notes ───────────────────────────────────────────────────
  Error: Error: Length of `path` must equal length of `new_path`
  Running git worktree remove --force \
    /home/runner/work/deep-learning-intro/deep-learning-intro/site/docs
  Running git worktree remove --force \
    /home/runner/work/deep-learning-intro/deep-learning-intro/site/built
  Execution halted
  Error: Process completed with exit code 1.
  ##[debug]Finishing: Deploy Site

I cannot reproduce this locally; it passes fine:

% R -e 'sandpaper::serve(quiet = FALSE, port = "3435")'

R version 4.3.2 (2023-10-31) -- "Eye Holes"
[...]

── Creating Images page ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Writing 'instructor/images.html'
Writing 'images.html'
── Creating Instructor Notes ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Writing 'instructor/instructor-notes.html'
Writing 'instructor-notes.html'
── Creating sitemap.xml ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

Output created: /Users/carstenschnober/Courses/teaching/deep-learning-intro/site/docs/index.html
Serving the directory /Users/carstenschnober/Courses/teaching/deep-learning-intro/site/docs at http://127.0.0.1:3435

Minor progress, I can now reproduce the issue locally:

% Rscript -e 'sandpaper:::ci_deploy(reset = TRUE)'
[...]
── Creating Images page ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Writing 'instructor/images.html'
Writing 'images.html'
── Creating Instructor Notes ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Error: Length of `path` must equal length of `new_path`
Running git worktree remove --force \
  /Users/carstenschnober/Courses/teaching/deep-learning-intro/site/docs
Running git worktree remove --force \
  /Users/carstenschnober/Courses/teaching/deep-learning-intro/site/built
Execution halted

carpentries-incubator / deep-learning-intro

Fix `Build and Deploy` workflow #458