build(deps-dev): bump postcss from 8.4.38 to 8.4.39

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.38 to 8.4.39.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.38...8.4.39)

---
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

@@ -56,7 +56,7 @@
     "eslint-plugin-mdx": "3.1.5",
     "eslint-plugin-simple-import-sort": "12.1.0",
     "mdx": "0.3.1",
-    "postcss": "8.4.38",
+    "postcss": "8.4.39",
     "prettier": "3.3.3",
     "remark": "15.0.1",
     "remark-cli": "12.0.1",