Build(deps-dev): Bump @storybook/addon-a11y from 6.4.8 to 6.4.19

Bumps [@storybook/addon-a11y](https://github.com/storybookjs/storybook/tree/HEAD/addons/a11y) from 6.4.8 to 6.4.19.
- [Release notes](https://github.com/storybookjs/storybook/releases)
- [Changelog](https://github.com/storybookjs/storybook/blob/v6.4.19/CHANGELOG.md)
- [Commits](https://github.com/storybookjs/storybook/commits/v6.4.19/addons/a11y)

---
updated-dependencies:
- dependency-name: "@storybook/addon-a11y"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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