Update dependency postcss-load-config to v4 (postcss#437)

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

Author: renovate[bot]

package.json

@@ -24,7 +24,7 @@
     "get-stdin": "^9.0.0",
     "globby": "^13.0.0",
     "picocolors": "^1.0.0",
-    "postcss-load-config": "^3.0.0",
+    "postcss-load-config": "^4.0.0",
     "postcss-reporter": "^7.0.0",
     "pretty-hrtime": "^1.0.3",
     "read-cache": "^1.0.0",