Update dependency postcss to v8.5.6 (#490)

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

Author: renovate[bot]

package-lock.json

@@ -26,7 +26,7 @@
     "css-loader": "7.1.2",
     "html-webpack-plugin": "5.6.3",
     "mini-css-extract-plugin": "2.9.2",
-    "postcss": "8.5.5",
+    "postcss": "8.5.6",
     "postcss-loader": "8.1.1",
     "sass": "1.89.2",
     "sass-loader": "16.0.5",