The current contrib deploy-hook fails if there is no `gh-pages` branch.
Change the CI order to disregard the old `gh-pages` branch first.
The `contrib` deploy-hook always creates a fresh `gh-pages` commit and
pushes it out. However, currently it relies on the old `gh-pages` branch
to exist, since it does not ignore errors when pruning it. Fortunately,
the code always creates a new orphan branch, since it does not want to
keep history for deployments. Therefore, we can simply use:
`git worktree --orphan -B <branch> <path>`
This will ensure to always create an orphan branch named `<branch>`, and
override an existing branch if it exists (see `-b` vs `-B`). Hence,
there is no need for us to prune the old branch, anymore.
Since we will recreate the branch on every push, we have to explicitly
specify the remote to push to. We no longer set up branch tracking.
Previously mdbook was bumped in #11646 for contrib.yml worflow
but main.yaml workflow. This makes the two in sync and also
upgrades to the latest 0.4.27. (Though there is nothing really
changed for application users as us)
