fix(@angular-devkit/build-angular): upgrade postcss to 8.5.12

This addresses GHSA-qx2v-qp2m-jg93

Fixes: #33067

Author: alan-agius4

packages/angular/build/package.json

@@ -54,7 +54,7 @@
     "jsdom": "26.1.0",
     "less": "4.4.0",
     "ng-packagr": "20.3.0",
-    "postcss": "8.5.6",
+    "postcss": "8.5.12",
     "rxjs": "7.8.2",
     "vitest": "3.2.4"
   },

packages/angular_devkit/build_angular/package.json

@@ -43,7 +43,7 @@
     "ora": "8.2.0",
     "picomatch": "4.0.4",
     "piscina": "5.1.3",
-    "postcss": "8.5.6",
+    "postcss": "8.5.12",
     "postcss-loader": "8.1.1",
     "resolve-url-loader": "5.0.0",
     "rxjs": "7.8.2",