chore(deps-dev): bump @storybook/addon-viewport from 5.3.21 to 6.4.9

Bumps [@storybook/addon-viewport](https://github.com/storybookjs/storybook/tree/HEAD/addons/viewport) from 5.3.21 to 6.4.9.
- [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/v6.4.9/addons/viewport)

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

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