Use deployment key in CI for manipulating Git repository

This allows CI to bypass the pull request requirement for pushing to `main`

.github/workflows/version-bump.yml

@@ -32,6 +32,8 @@ jobs:
       # ----------------------------------------------------------------------- Checkout
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          ssh-key: ${{secrets.CI_DEPLOYMENT_KEY}}
 
       # ----------------------------------------------------------------------- Override the submodule URL
       # This is to support testing release automation in forks, it is disabled for the canonical docs repo