Commands to trigger optional tests are checking out main and not current branch

[loicdiridollou]

I will fix it, we need to pass the ref of the branch when running the checkout action.
cf https://github.com/pandas-dev/pandas-stubs/actions/runs/12682308972/job/35347482421

Run actions/checkout@v4
Syncing repository: pandas-dev/pandas-stubs
Getting Git version info
Temporarily overriding HOME='/home/runner/work/_temp/449e1c2d-dee6-41fc-8c57-482fcf8bdcbc' before making global git config changes
Adding repository directory to the temporary git global config as a safe directory
/usr/bin/git config --global --add safe.directory /home/runner/work/pandas-stubs/pandas-stubs
Deleting the contents of '/home/runner/work/pandas-stubs/pandas-stubs'
Initializing the repository
Disabling automatic garbage collection
Setting up auth
Fetching the repository
Determining the checkout info
/usr/bin/git sparse-checkout disable
/usr/bin/git config --local --unset-all extensions.worktreeConfig
Checking out the ref
  /usr/bin/git checkout --progress --force -B main refs/remotes/origin/main
  Switched to a new branch 'main'
  branch 'main' set up to track 'origin/main'.
/usr/bin/git log -1 --format=%H
d410f2efd08acf4c3c7357db25de496[19](https://github.com/pandas-dev/pandas-stubs/actions/runs/12682308972/job/35347482421#step:2:20)5f60930