Bump postcss from 8.4.26 to 8.4.31 in /ui-tests (#441)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.26 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@8.4.26...8.4.31)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
...

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

Author: dependabot[bot]

ui-tests/yarn.lock

@@ -3277,13 +3277,13 @@ __metadata:
   linkType: hard
 
 "postcss@npm:^8.3.11":
-  version: 8.4.26
-  resolution: "postcss@npm:8.4.26"
+  version: 8.4.31
+  resolution: "postcss@npm:8.4.31"
   dependencies:
     nanoid: ^3.3.6
     picocolors: ^1.0.0
     source-map-js: ^1.0.2
-  checksum: 1cf08ee10d58cbe98f94bf12ac49a5e5ed1588507d333d2642aacc24369ca987274e1f60ff4cbf0081f70d2ab18a5cd3a4a273f188d835b8e7f3ba381b184e57
+  checksum: 1d8611341b073143ad90486fcdfeab49edd243377b1f51834dc4f6d028e82ce5190e4f11bb2633276864503654fb7cab28e67abdc0fbf9d1f88cad4a0ff0beea
   languageName: node
   linkType: hard