fix: Incorrect fetch for `baseRef`

[rschristian]

 /usr/bin/git fetch -n origin main
  From https://github.com/preactjs/preact
   * branch              main       -> FETCH_HEAD
   * [new branch]        main       -> origin/main
  successfully fetched base.ref
  checking out and building base commit
  /usr/bin/git reset --hard main
  fatal: ambiguous argument 'main': unknown revision or path not in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'

• Logs

As the repo is a shallow clone, fetches will only update the remote branch tracking the currently cloned branch, i.e., git fetch <another branch> won't have any effect (to my understanding). Providing a local branch to track the remote from will fix this, however.

Simple demonstration of the issue:

git clone [email protected]:preactjs/preact.git --depth=1
cd preact
git fetch -n origin disable-rendering-on-unmount # fetch will succeed, but not affect the repo
git reset --hard disable-rendering-on-unmount # will fail with the same error as shown above

git fetch -n origin disable-rendering-on-unmount:disable-rendering-on-unmount
git reset --hard disable-rendering-on-unmount # will succeed