Problem with Documenter Clean Up

General Usage
1

I am not able to use the Doc Preview Cleanup, as explained here.

Using the very same workflow they have described, I obtain the following error message

  git config user.name "Documenter.jl"
  git config user.email "documenter@juliadocs.github.io"
  git rm -rf "previews/PR$PRNUM"
  git commit -m "delete preview"
  git branch gh-pages-new $(echo "delete history" | git commit-tree HEAD^{tree})
  shell: /usr/bin/bash -e {0}
  env:
    PRNUM: 105
fatal: pathspec 'previews/PR105' did not match any files
Error: Process completed with exit code 128.

Thank you for your help,
Marco Bonici