chore(deps-dev): bump mini-css-extract-plugin in /superset-frontend

Bumps [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) from 2.3.0 to 2.4.5.
- [Release notes](https://github.com/webpack-contrib/mini-css-extract-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/mini-css-extract-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/mini-css-extract-plugin@v2.3.0...v2.4.5)

---
updated-dependencies:
- dependency-name: mini-css-extract-plugin
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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