Bump postcss from 8.4.23 to 8.4.31 (PlasmoHQ#83)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.23 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.23...8.4.31)

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

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Author: dependabot[bot]

package.json

@@ -22,7 +22,7 @@
     "next-seo": "6.0.0",
     "nextra": "2.4.1",
     "nextra-theme-docs": "2.4.1",
-    "postcss": "8.4.23",
+    "postcss": "8.4.31",
     "prism-react-renderer": "1.3.5",
     "prismjs": "1.29.0",
     "react": "18.2.0",