Bump postcss from 8.4.6 to 8.4.31 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.6 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/8.4.6...8.4.31)

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

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

frontend/yarn.lock

@@ -2739,7 +2739,7 @@ mz@^2.7.0:
     object-assign "^4.0.1"
     thenify-all "^1.0.0"
 
-nanoid@^3.2.0, nanoid@^3.3.6:
+nanoid@^3.3.6:
   version "3.3.6"
   resolved "https://registry.npmjs.org/nanoid/-/nanoid-3.3.6.tgz"
   integrity sha512-BGcqMMJuToF7i1rt+2PWSNVnWIkGCU78jBG3RxO/bZlnZPK2Cmi2QaffxGO/2RvWi9sL+FAiRiXMgsyxQ1DIDA==
@@ -2979,19 +2979,10 @@ postcss-value-parser@^4.0.0, postcss-value-parser@^4.2.0:
   resolved "https://registry.npmjs.org/postcss-value-parser/-/postcss-value-parser-4.2.0.tgz"
   integrity sha512-1NNCs6uurfkVbeXG4S8JFT9t19m45ICnif8zWLd5oPSZ50QnwMfK+H3jv408d4jw/7Bttv5axS5IiHoLaVNHeQ==
 
-postcss@8.4.6:
-  version "8.4.6"
-  resolved "https://registry.npmjs.org/postcss/-/postcss-8.4.6.tgz"
-  integrity sha512-OovjwIzs9Te46vlEx7+uXB0PLijpwjXGKXjVGGPIGubGpq7uh5Xgf6D6FiJ/SzJMBosHDp6a2hiXOS97iBXcaA==
-  dependencies:
-    nanoid "^3.2.0"
-    picocolors "^1.0.0"
-    source-map-js "^1.0.2"
-
-postcss@^8.4.23, postcss@^8.4.25:
-  version "8.4.26"
-  resolved "https://registry.npmjs.org/postcss/-/postcss-8.4.26.tgz"
-  integrity sha512-jrXHFF8iTloAenySjM/ob3gSj7pCu0Ji49hnjqzsgSRa50hkWCKD0HQ+gMNJkW38jBI68MpAAg7ZWwHwX8NMMw==
+postcss@8.4.31, postcss@^8.4.23, postcss@^8.4.25:
+  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"