test(docs-infra): add proxy to fake images in tests (#35741)

Previously, when running the unit tests for aio on Windows, many 404s
are logged for images, resulting in progress logs being spread over
multiple lines. This commit fixes this by adding a `proxy` to point
the fake image to a real image within the `src` folder.

Closes #29775

PR Close #35741

aio/karma.conf.js

@@ -14,6 +14,9 @@ module.exports = function (config) {
       require('@angular-devkit/build-angular/plugins/karma'),
       {'reporter:jasmine-seed': ['type', JasmineSeedReporter]},
     ],
+    proxies: {
+      '/dummy/image': 'src/assets/images/logos/angular/angular.png',
+    },
     client: {
       clearContext: false,  // leave Jasmine Spec Runner output visible in browser
       jasmine: {

aio/src/app/custom-elements/announcement-bar/announcement-bar.component.spec.ts

@@ -88,7 +88,7 @@ describe('AnnouncementBarComponent', () => {
   describe('rendering', () => {
     beforeEach(() => {
       component.announcement = {
-        imageUrl: 'link/to/image',
+        imageUrl: 'dummy/image',
         linkUrl: 'link/to/website',
         message: 'this is an <b>important</b> message',
         endDate: '2018-03-01',
@@ -102,7 +102,7 @@ describe('AnnouncementBarComponent', () => {
     });
 
     it('should display an image', () => {
-      expect(element.querySelector('img')!.src).toContain('link/to/image');
+      expect(element.querySelector('img')!.src).toContain('dummy/image');
     });
 
     it('should display a link', () => {