chore(deps-dev): bump postcss in /packages/taro-ui-demo

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:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

packages/taro-ui-demo/package.json

@@ -78,7 +78,7 @@
     "eslint-plugin-import": "^2.12.0",
     "eslint-plugin-react": "^7.8.2",
     "eslint-plugin-react-hooks": "^4.2.0",
-    "postcss": "^8.4.18",
+    "postcss": "^8.4.31",
     "react-refresh": "^0.11.0",
     "sass": "^1.49.9",
     "stylelint": "^14.4.0",

packages/taro-ui-demo/yarn.lock

@@ -3969,7 +3969,7 @@ class-utils@^0.3.5:
     isobject "^3.0.0"
     static-extend "^0.1.1"
 
-classnames@^2.2.5, classnames@^2.2.6:
+classnames@^2.2.5:
   version "2.3.2"
   resolved "https://registry.yarnpkg.com/classnames/-/classnames-2.3.2.tgz#351d813bf0137fcc6a76a16b88208d2560a0d924"
   integrity sha512-CSbhY4cFEJRe6/GQzIk5qXZ4Jeg5pcsP7b5peFSDpffpe1cqjASH/n9UTjBwOp6XpMSTwQ8Za2K5V02ueA7Tmw==