Bump postcss from 8.5.1 to 8.5.6 (#3215)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.6
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]

package.json

@@ -40,7 +40,7 @@
     "eslint": "^8.57.0",
     "eslint-plugin-jest": "^28.11.0",
     "eslint-plugin-svelte": "^2.46.1",
-    "postcss": "^8.5.1",
+    "postcss": "^8.5.6",
     "prettier": "3.3.3",
     "prettier-plugin-astro": "^0.14.1",
     "prettier-plugin-svelte": "^3.3.3",