build(deps): bump yaml and postcss-loader in /web

Removes [yaml](https://github.com/eemeli/yaml). It's no longer used after updating ancestor dependency [postcss-loader](https://github.com/webpack-contrib/postcss-loader). These dependencies need to be updated together.


Removes `yaml`

Updates `postcss-loader` from 4.1.0 to 7.2.4
- [Release notes](https://github.com/webpack-contrib/postcss-loader/releases)
- [Changelog](https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/postcss-loader/compare/v4.1.0...v7.2.4)

---
updated-dependencies:
- dependency-name: yaml
  dependency-type: indirect
- dependency-name: postcss-loader
  dependency-type: direct:development
...

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

web/package.json

@@ -33,7 +33,7 @@
     "eslint-plugin-jsdoc": "^30.7.8",
     "html-webpack-plugin": "^4.5.0",
     "mini-css-extract-plugin": "^1.3.1",
-    "postcss-loader": "^4.1.0",
+    "postcss-loader": "^7.2.4",
     "regenerator-runtime": "^0.13.7",
     "sass": "^1.29.0",
     "sass-loader": "^10.1.0",