Bump postcss-loader from 7.1.0 to 7.3.0

Bumps [postcss-loader](https://github.com/webpack-contrib/postcss-loader) from 7.1.0 to 7.3.0.
- [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@v7.1.0...v7.3.0)

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

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

package.json

@@ -25,7 +25,7 @@
         "highlight.js": "^11.8.0",
         "leaflet": "^1.9.3",
         "postcss": "^8.4.21",
-        "postcss-loader": "^7.1.0",
+        "postcss-loader": "^7.3.0",
         "prop-types": "^15.8.1",
         "react": "^18.2.0",
         "react-dom": "^18.2.0",