Bump postcss from 8.4.29 to 8.4.31 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.29 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.29...8.4.31)

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

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

frontend/pnpm-lock.yaml

@@ -1940,8 +1940,8 @@ packages:
     engines: {node: '>=8.6'}
     dev: true
 
-  /postcss@8.4.29:
-    resolution: {integrity: sha512-cbI+jaqIeu/VGqXEarWkRCCffhjgXc0qjBtXpqJhTBohMUjUQnbBr0xqX3vEKudc4iviTewcJo5ajcec5+wdJw==}
+  /postcss@8.4.31:
+    resolution: {integrity: sha512-PS08Iboia9mts/2ygV3eLpY5ghnUcfLV/EXTOW1E2qYxJKGGBUtNjN76FYHnMs36RmARn41bC0AZmn+rR0OVpQ==}
     engines: {node: ^10 || ^12 || >=14}
     dependencies:
       nanoid: 3.3.6
@@ -2273,7 +2273,7 @@ packages:
     dependencies:
       '@types/node': 20.6.2
       esbuild: 0.18.20
-      postcss: 8.4.29
+      postcss: 8.4.31
       rollup: 3.29.2
     optionalDependencies:
       fsevents: 2.3.3