Fix vendoring PRs for stable branches (1.3)

This is a backport of the PR duckdb#262 to `v1.3-ossivalis` stable branch.

Nightly import of DuckDB engine sources ("vendoring") is performed by
creating PRs on `vendoring-<branch>` base branches. After the tests are
passed the PR is merged and `vendoring-<branch>` is re-created to be
used in subsequent imports.

This change fixes the vendoring branch re-creation to place it not
always on the `main` branch, but on the correct branch (either `main` or
stable one line `v1.3-ossivalis`).

Author: staticlibs

.github/workflows/Java.yml

@@ -434,7 +434,7 @@ jobs:
         run: |
             # Delete vendoring-${{ github.base_ref }} branch and re-create it for future PRs
             git push --delete origin vendoring-${{ github.base_ref }}
-            git checkout --track origin/main
+            git checkout --track origin/${{ github.base_ref }}
             git pull --ff-only
             git branch vendoring-${{ github.base_ref }}
             git push origin vendoring-${{ github.base_ref }}