Bump @nx/storybook from 19.5.7 to 20.4.6

Bumps [@nx/storybook](https://github.com/nrwl/nx/tree/HEAD/packages/storybook) from 19.5.7 to 20.4.6.
- [Release notes](https://github.com/nrwl/nx/releases)
- [Commits](https://github.com/nrwl/nx/commits/20.4.6/packages/storybook)

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

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