Update dependency postcss to v8.4.31 [SECURITY]

package.json

@@ -22,7 +22,7 @@
     "@canonical/global-nav": "3.2.4",
     "autoprefixer": "10.4.14",
     "concurrently": "8.0.1",
-    "postcss": "8.4.23",
+    "postcss": "8.4.31",
     "postcss-cli": "10.1.0",
     "prettier": "2.8.8",
     "sass": "1.62.1",

yarn.lock

@@ -1361,10 +1361,10 @@ [email protected]:
     picocolors "^1.0.0"
     source-map-js "^1.0.2"
 
-[email protected].23:
-  version "8.4.23"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.4.23.tgz#df0aee9ac7c5e53e1075c24a3613496f9e6552ab"
-  integrity sha512-bQ3qMcpF6A/YjR55xtoTr0jGOlnPOKAIMdOWiv0EIT6HVPEaJiJB4NLljSbiHoC2RX7DN5Uvjtpbg1NPdwv1oA==
+[email protected].31:
+  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"