Bump @nx/storybook from 19.5.7 to 21.6.4

Bumps [@nx/storybook](https://github.com/nrwl/nx/tree/HEAD/packages/storybook) from 19.5.7 to 21.6.4.
- [Release notes](https://github.com/nrwl/nx/releases)
- [Commits](https://github.com/nrwl/nx/commits/21.6.4/packages/storybook)

---
updated-dependencies:
- dependency-name: "@nx/storybook"
  dependency-version: 21.6.4
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]