Bump @storybook/addon-storysource from 5.3.0-rc.12 to 6.2.9

Bumps [@storybook/addon-storysource](https://github.com/storybookjs/storybook/tree/HEAD/addons/storysource) from 5.3.0-rc.12 to 6.2.9.
- [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/v6.2.9/addons/storysource)

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

Author: dependabot-preview[bot]