Bump mini-css-extract-plugin from 2.5.3 to 2.6.0 in /assets

Bumps [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) from 2.5.3 to 2.6.0.
- [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@v2.5.3...v2.6.0)

---
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>

assets/package.json

@@ -27,7 +27,7 @@
     "css-loader": "^6.6.0",
     "css-minimizer-webpack-plugin": "^3.4.1",
     "hard-source-webpack-plugin": "^0.13.1",
-    "mini-css-extract-plugin": "^2.5.3",
+    "mini-css-extract-plugin": "^2.6.0",
     "node-sass-glob-importer": "^5.3.2",
     "postcss": "^8.4.8",
     "sass": "^1.49.9",