Bump css-loader from 5.2.6 to 6.3.0 in /assets

Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 5.2.6 to 6.3.0.
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/css-loader@v5.2.6...v6.3.0)

---
updated-dependencies:
- dependency-name: css-loader
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

assets/package.json

@@ -22,7 +22,7 @@
     "@types/phoenix_live_view": "^0.15.0",
     "babel-loader": "^8.2.2",
     "copy-webpack-plugin": "^9.0.1",
-    "css-loader": "^5.2.6",
+    "css-loader": "^6.3.0",
     "css-minimizer-webpack-plugin": "^3.0.2",
     "hard-source-webpack-plugin": "^0.13.1",
     "mini-css-extract-plugin": "^2.3.0",