chore(deps): bump postcss from 8.4.27 to 8.4.31 (#12341)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.27 to 8.4.31.
- [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/8.4.27...8.4.31)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:production
...

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

packages/vant-cli/package.json

@@ -70,7 +70,7 @@
     "markdown-it-anchor": "^8.6.4",
     "nano-staged": "^0.8.0",
     "picocolors": "^1.0.0",
-    "postcss": "^8.4.23",
+    "postcss": "^8.4.31",
     "postcss-load-config": "^4.0.1",
     "prettier": "^3.0.0",
     "terser": "^5.19.2",