build(deps-dev): Bump @storybook/addon-essentials from 6.4.19 to 6.4.…

…21 (#1976)

Bumps [@storybook/addon-essentials](https://github.com/storybookjs/storybook/tree/HEAD/addons/essentials) from 6.4.19 to 6.4.21.
- [Release notes](https://github.com/storybookjs/storybook/releases)
- [Changelog](https://github.com/storybookjs/storybook/blob/next/CHANGELOG.md)
- [Commits](https://github.com/storybookjs/storybook/commits/v6.4.21/addons/essentials)

---
updated-dependencies:
- dependency-name: "@storybook/addon-essentials"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Isaac Garfinkle <isaac@truss.works>