chore(deps): bump @storybook/theming from 7.0.6 to 7.0.20

Bumps [@storybook/theming](https://github.com/storybookjs/storybook/tree/HEAD/code/lib/theming) from 7.0.6 to 7.0.20.
- [Release notes](https://github.com/storybookjs/storybook/releases)
- [Changelog](https://github.com/storybookjs/storybook/blob/v7.0.20/CHANGELOG.md)
- [Commits](https://github.com/storybookjs/storybook/commits/v7.0.20/code/lib/theming)

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

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