Adding in reference to #1239.
@grafana/docs-oncall should be tagged as a PR reviewer for changes to
`/docs` rahter than @grafana/grafana-oncall-backend.
# What this PR does
There is no need to add `@grafana/grafana-oncall-backend` as a PR
reviewer when `CHANGELOG.md` is updated
## Which issue(s) this PR fixes
## Checklist
- [ ] Tests updated (N/A)
- [ ] Documentation added (N/A)
- [ ] `CHANGELOG.md` updated (N/A)