ci: Bring back stepwise vendoring

.github/workflows/vendor.yaml

@@ -35,33 +35,29 @@ jobs:
 
       - uses: ./.github/workflows/git-identity
 
-      - name: Check out or create vendor branch
+      - name: Vendor sources
         id: vendor
         run: |
-          set -x
-          if ! git checkout vendor; then
-            git checkout -b vendor
-            git push -u origin HEAD
+          git pull --rebase
+          ./vendor-one.sh .git/duckdb
+          rm -rf .git/duckdb
+          git push --dry-run
+          # Check if ahead of upstream branch
+          # If yes, set a step output
+          if [ $(git rev-list HEAD...origin/main --count) -gt 0 ]; then
+            # Avoid set-output, it's deprecated
+            echo "vendor=ok" >> "$GITHUB_OUTPUT"
           fi
 
-      - name: Vendor sources
+      - name: Create PR
+        if: steps.vendor.outputs.vendor != ''
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          git push --dry-run
-
-          # Repeat indefinitely until all commits have been vendored
-          # https://stackoverflow.com/a/13252187/946850
-          while :; do
-            ./vendor-one.sh .git/duckdb
-            # Check if ahead of upstream branch
-            # If yes, push and run workflow
-            if [ $(git rev-list HEAD...origin/vendor --count) -gt 0 ]; then
-              git push -u origin HEAD
-              gh workflow run rcc -f ref=vendor
-            else
-              break
-            fi
-          done
-
-          rm -rf .git/duckdb
+          set -x
+          git checkout -b vendor
+          if git push -u origin HEAD; then
+            gh pr create --fill-first
+            gh workflow run rcc -f ref=vendor
+            gh pr merge --auto --squash
+          fi