Bump postcss from 8.3.6 to 8.4.31 in /canvas_modules/harness (#1586)

Bumps [postcss](https://github.com/postcss/postcss) from 8.3.6 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@8.3.6...8.4.31)

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

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

canvas_modules/harness/package.json

@@ -68,7 +68,7 @@
     "mini-css-extract-plugin": "0.11.2",
     "object-assign": "4.1.1",
     "path": "0.12.7",
-    "postcss": "8.3.6",
+    "postcss": "8.4.31",
     "postcss-loader": "4.3.0",
     "prop-types": "15.7.2",
     "react": "18.2.0",