fix: Update helm to version 2.16.6

We were previously on 2.16.3. The releases since then have all been bugfix releases. In particular, this should include a fix for checking .Capabilties in templates, allowing us to render different resources based on the kubernetes version.

See

• https://github.com/helm/helm/releases/tag/v2.16.6
• https://github.com/helm/helm/releases/tag/v2.16.5
• https://github.com/helm/helm/releases/tag/v2.16.4