chore: make pypi release workflow perform checkout (bazel-contrib#3371)

The pypi workflow step is now a separate job, so it doesn't start with
the code checkout
done already. Run the checkout action so it is available so the bazel
upload
command can run.

Author: rickeylev

.github/workflows/release.yml

@@ -70,6 +70,10 @@ jobs:
     needs: publish_bcr
     runs-on: ubuntu-latest
     steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+        with:
+          ref: ${{ github.tag_name || github.ref_name }}
       - if: github.event_name == 'push' || github.event.inputs.publish_to_pypi
         env:
           # This special value tells pypi that the user identity is supplied within the token