meta: fix GHA workflow for prereleases

.github/workflows/release-beta-candidate.yml

@@ -14,7 +14,7 @@ jobs:
       - name: Checkout sources
         uses: actions/checkout@v3
         with:
-          branch: release
+          branch: release-beta
       - name: Rebase
         run: |
           git fetch origin ${{ env.BETA_BRANCH }} --depth=1