chore: make build process a single script to run

.github/workflows/ci.yml

@@ -68,6 +68,12 @@ jobs:
       - name: Build
         run: pnpm run build
 
+      - name: Ensure staging a release works.
+        working-directory: codex-cli
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: pnpm stage-release
+
       - name: Ensure README.md contains only ASCII and certain Unicode code points
         run: ./scripts/asciicheck.py README.md
       - name: Check README ToC