Bump postcss from 8.4.26 to 8.4.31 in /client

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](https://github.com/postcss/postcss/compare/8.4.26...8.4.31)

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

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

client/yarn.lock

@@ -3135,19 +3135,10 @@ popper.js@1.16.1-lts:
   resolved "https://registry.yarnpkg.com/popper.js/-/popper.js-1.16.1-lts.tgz#cf6847b807da3799d80ee3d6d2f90df8a3f50b05"
   integrity sha512-Kjw8nKRl1m+VrSFCoVGPph93W/qrSO7ZkqPpTf7F4bk/sqcfWK019dWBUpE/fBOsOQY1dks/Bmcbfn1heM/IsA==
 
-postcss@^8.4.18:
-  version "8.4.26"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.26.tgz#1bc62ab19f8e1e5463d98cf74af39702a00a9e94"
-  integrity sha512-jrXHFF8iTloAenySjM/ob3gSj7pCu0Ji49hnjqzsgSRa50hkWCKD0HQ+gMNJkW38jBI68MpAAg7ZWwHwX8NMMw==
-  dependencies:
-    nanoid "^3.3.6"
-    picocolors "^1.0.0"
-    source-map-js "^1.0.2"
-
-postcss@^8.4.23:
-  version "8.4.27"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.27.tgz#234d7e4b72e34ba5a92c29636734349e0d9c3057"
-  integrity sha512-gY/ACJtJPSmUFPDCHtX78+01fHa64FaU4zaaWfuh1MhGJISufJAH4cun6k/8fwsHYeK4UQmENQK+tRLCFJE8JQ==
+postcss@^8.4.18, postcss@^8.4.23:
+  version "8.4.31"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.31.tgz#92b451050a9f914da6755af352bdc0192508656d"
+  integrity sha512-PS08Iboia9mts/2ygV3eLpY5ghnUcfLV/EXTOW1E2qYxJKGGBUtNjN76FYHnMs36RmARn41bC0AZmn+rR0OVpQ==
   dependencies:
     nanoid "^3.3.6"
     picocolors "^1.0.0"