Add helm dependency build step to release workflow (#279)

## Summary
- Add `helm dependency build` before `helm package` in the release
workflow's helm job
- This fixes the controller Helm chart push which has been failing since
cert-manager was added as an optional subchart dependency
- The other helm workflows (`helm.yml`, `helm-validate.yml`,
`helm-image-check.yml`) already have this step — `release.yml` was
missed

## Context
The v1.5.0, v1.5.1, and v1.5.2 releases all failed to push the
controller Helm chart to OCI with:
```
Error: found in Chart.yaml, but missing in charts/ directory: cert-manager
```

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Shivs11

.github/workflows/release.yml

@@ -139,6 +139,9 @@ jobs:
           git commit -m "Bump chart version to $NEW_VERSION [skip ci]"
           git push
 
+      - name: Build chart dependencies
+        run: helm repo add jetstack https://charts.jetstack.io && helm dependency build ./helm/temporal-worker-controller
+
       - name: Package and Push Helm charts
         run: |
           # Use version from previous step