Bump postcss from 8.3.11 to 8.4.31 in /src/OpenMod.Plugins

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.11 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@8.3.11...8.4.31)

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

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

src/OpenMod.Plugins/package.json

@@ -16,7 +16,7 @@
     "dependencies": {
         "@tailwindcss/typography": "^0.4.1",
         "autoprefixer": "^10.4.0",
-        "postcss": "^8.3.11",
+        "postcss": "^8.4.31",
         "postcss-cli": "^9.0.1",
         "tailwindcss": "^2.2.19"
     }