fix(@angular-devkit/build-angular): upgrade postcss to 8.5.23

This addresses GHSA-fxqj-rqcc-2cmp

TAG=agy

CONV=63a146aa-f34e-4200-88d1-90537150adb0

Author: alan-agius4

packages/angular_devkit/build_angular/package.json

@@ -42,7 +42,7 @@
     "ora": "9.3.0",
     "picomatch": "4.0.4",
     "piscina": "5.2.0",
-    "postcss": "8.5.12",
+    "postcss": "8.5.23",
     "postcss-loader": "8.2.0",
     "resolve-url-loader": "5.0.0",
     "rxjs": "7.8.2",