update docs to use latest checkout action

update docs to use latest checkout action

I can only get this to work when setting `fetch-depth: 0`. Otherwise, I see this error

```
push fixes
  /usr/bin/git config user.name pre-commit
  /usr/bin/git config user.email pre-commit@example.com
  /usr/bin/git checkout HEAD -b pre-commit-gha
  M	README.md
  Switched to a new branch 'pre-commit-gha'
  /usr/bin/git commit -am pre-commit fixes
  [pre-commit-gha 800dbc6] pre-commit fixes
   1 file changed, 1 insertion(+), 1 deletion(-)
  /usr/bin/git remote set-url origin ***github.com/***.git
  /usr/bin/git push origin HEAD
  To https://github.com/***.git
   ! [rejected]        HEAD -> pre-commit-gha (fetch first)
  error: failed to push some refs to 'https://github.com/***.git'
  hint: Updates were rejected because the remote contains work that you do
  hint: not have locally. This is usually caused by another repository pushing
  hint: to the same ref. You may want to first integrate the remote changes
  hint: (e.g., 'git pull ...') before pushing again.
```