Update dependency postcss to v8.5.5

Author: renovate[bot]

package.json

@@ -66,7 +66,7 @@
     "eslint-plugin-prettier": "4.2.1",
     "eslint-plugin-react": "7.32.2",
     "gatsby-plugin-no-sourcemaps": "5.13.0",
-    "postcss": "8.4.31",
+    "postcss": "8.5.5",
     "postcss-import": "^15.1.0",
     "prettier": "2.8.8",
     "prettier-plugin-tailwindcss": "^0.4.0",