test(@angular-devkit/build-angular): correctly disable caching in unit-tests

The unit-tests where intended to not use build caching to better ensure test isolation. However, the configuration format was incorrect and did not disable the build caching.

Author: clydin

packages/angular_devkit/build_angular/test/hello-world-app/angular.json

@@ -3,7 +3,9 @@
   "version": 1,
   "newProjectRoot": "./projects",
   "cli": {
-    "enabled": false
+    "cache": {
+      "enabled": false
+    }
   },
   "schematics": {},
   "targets": {},

packages/angular_devkit/build_angular/test/hello-world-lib/angular.json

@@ -2,7 +2,9 @@
   "$schema": "../../../../packages/angular_devkit/core/src/workspace/workspace-schema.json",
   "version": 1,
   "cli": {
-    "enabled": false
+    "cache": {
+      "enabled": false
+    }
   },
   "projects": {
     "lib": {