Bump postcss from 8.4.17 to 8.4.18

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.17 to 8.4.18.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.17...8.4.18)

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

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

package.json

@@ -60,7 +60,7 @@
     "html-webpack-plugin": "^5.5.0",
     "jest": "^26.6.3",
     "mini-css-extract-plugin": "^2.6.1",
-    "postcss": "^8.4.17",
+    "postcss": "^8.4.18",
     "postcss-loader": "^7.0.1",
     "style-loader": "^3.3.1",
     "terser-webpack-plugin": "^5.3.6",