Build(deps): Bump @wordpress/blocks from 15.12.0 to 15.13.0 (#586)

Bumps [@wordpress/blocks](https://github.com/WordPress/gutenberg/tree/HEAD/packages/blocks) from 15.12.0 to 15.13.0.
- [Release notes](https://github.com/WordPress/gutenberg/releases)
- [Changelog](https://github.com/WordPress/gutenberg/blob/trunk/packages/blocks/CHANGELOG.md)
- [Commits](https://github.com/WordPress/gutenberg/commits/@wordpress/blocks@15.13.0/packages/blocks)

---
updated-dependencies:
- dependency-name: "@wordpress/blocks"
  dependency-version: 15.13.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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