Update release workflow to target charts/nginx-ingress folder

[shaun-nx]

Now that our Helm related files are in charts/nginx-ingress our release-pr.yaml workflow file needs to be updated to ensure these files are updated for each release.

See https://github.com/nginxinc/kubernetes-ingress/pull/4278/files#diff-6d2776058621d57e67ee850e7db85691f8747f8bfa43021c3eb0663e78c8f2e8 for details on what exactly needs to be changed.

### Tasks
- [x] Add `charts/nginx-ingress/values.schema.json` to the list of files that require IC_VERSION updates

[github-actions]

Hi @shaun-nx thanks for reporting!

Be sure to check out the docs and the Contributing Guidelines while you wait for a human to take a look at this 🙂

Cheers!