Bump @google-cloud/storage from 7.19.0 to 7.21.0 (#320)

Bumps [@google-cloud/storage](https://github.com/googleapis/google-cloud-node/tree/HEAD/handwritten/storage) from 7.19.0 to 7.21.0.
- [Release notes](https://github.com/googleapis/google-cloud-node/releases)
- [Changelog](https://github.com/googleapis/google-cloud-node/blob/main/handwritten/storage/CHANGELOG.md)
- [Commits](https://github.com/googleapis/google-cloud-node/commits/storage-v7.21.0/handwritten/storage)

---
updated-dependencies:
- dependency-name: "@google-cloud/storage"
  dependency-version: 7.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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