build(deps-dev): bump postcss-loader from 7.3.4 to 8.1.1 (#429)

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 7.3.4 to 8.1.1.
- [Release notes](https://github.com/webpack-contrib/postcss-loader/releases)
- [Changelog](https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/postcss-loader@v7.3.4...v8.1.1)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -60,7 +60,7 @@
     "jest": "^29.4.1",
     "jest-environment-jsdom": "^29.4.2",
     "lint-staged": "^15.2.0",
-    "postcss-loader": "^7.2.1",
+    "postcss-loader": "^8.1.1",
     "prettier": "^3.0.3",
     "sass": "^1.34.0",
     "spritesmith": "~3.4.0",