Bump postcss from 8.5.6 to 8.5.15

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.6 to 8.5.15.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.6...8.5.15)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.15
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

package-lock.json

@@ -89,7 +89,7 @@
     "dotenv": "^17.2.3",
     "gh-pages": "^6.1.1",
     "lighthouse": "^12.1.0",
-    "postcss": "^8.4.47",
+    "postcss": "^8.5.15",
     "tailwindcss": "^3.4.12"
   },
   "browserslist": {