Bump @storybook/vue from 5.3.19 to 6.0.21

Bumps [@storybook/vue](https://github.com/storybookjs/storybook/tree/HEAD/app/vue) from 5.3.19 to 6.0.21.
- [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/v6.0.21/app/vue)

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

Author: dependabot-preview[bot]