chore: make pypi release workflow perform checkout (#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.

(cherry picked from commit cf594f780c91f13d48e77faad34df48ac57398da)

.github/workflows/release.yml

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 0d24d79..94c4d82 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -70,6 +70,10 @@
     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