Update dependency postcss to ^8.4.20 (#628)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package-lock.json

@@ -82,7 +82,7 @@
     "es-module-lexer": "^1.1.0",
     "esbuild": "^0.16.7",
     "mime": "^3.0.0",
-    "postcss": "^8.4.19",
+    "postcss": "^8.4.20",
     "puppeteer": "^16.2.0",
     "rollup": "^2.79.1",
     "rollup-plugin-postcss": "^4.0.2",