ci: rebase onto remote ref

.github/workflows/update-rust-overlay.yml

@@ -25,7 +25,7 @@ jobs:
           git config user.email "[email protected]"
           git add flake.lock
           git commit -m "build: update rust-overlay"
-          git rebase main
+          git rebase origin/main
       - name: Push changes
         if: steps.commit.outcome == 'success'
         uses: ad-m/github-push-action@master