workflows/prepare-release-branch: point to a branch with the same on contrib repo

Author: xrmx

.github/workflows/prepare-release-branch.yml

@@ -82,6 +82,11 @@ jobs:
       - name: Update version
         run: .github/scripts/update-version.sh $STABLE_VERSION $UNSTABLE_VERSION
 
+      - name: Update contrib sha to match a branch with the same name of this
+        run: |
+          pip install ruamel.yaml
+          python3 scripts/update_sha.py -b $RELEASE_BRANCH_NAME
+
       - name: Update the change log with the approximate release date
         run: |
           date=$(date "+%Y-%m-%d")