build(deps-dev): bump @wordpress/block-editor from 15.5.0 to 15.6.0

Bumps [@wordpress/block-editor](https://github.com/WordPress/gutenberg/tree/HEAD/packages/block-editor) from 15.5.0 to 15.6.0.
- [Release notes](https://github.com/WordPress/gutenberg/releases)
- [Changelog](https://github.com/WordPress/gutenberg/blob/trunk/packages/block-editor/CHANGELOG.md)
- [Commits](https://github.com/WordPress/gutenberg/commits/@wordpress/block-editor@15.6.0/packages/block-editor)

---
updated-dependencies:
- dependency-name: "@wordpress/block-editor"
  dependency-version: 15.6.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]