chore(deps): bump sigs.k8s.io/structured-merge-diff/v6 (#818)

Bumps [sigs.k8s.io/structured-merge-diff/v6](https://github.com/kubernetes-sigs/structured-merge-diff) from 6.3.2 to 6.4.0.
- [Release notes](https://github.com/kubernetes-sigs/structured-merge-diff/releases)
- [Changelog](https://github.com/kubernetes-sigs/structured-merge-diff/blob/master/RELEASE.md)
- [Commits](https://github.com/kubernetes-sigs/structured-merge-diff/compare/v6.3.2...v6.4.0)

---
updated-dependencies:
- dependency-name: sigs.k8s.io/structured-merge-diff/v6
  dependency-version: 6.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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