build(deps-dev): bump @wordpress/blocks from 15.8.0 to 15.9.0

Bumps [@wordpress/blocks](https://github.com/WordPress/gutenberg/tree/HEAD/packages/blocks) from 15.8.0 to 15.9.0.
- [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/[email protected]/packages/blocks)

---
updated-dependencies:
- dependency-name: "@wordpress/blocks"
  dependency-version: 15.9.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]