docs: update testing doc example style for HostListener (#26372)

HostListener is preferred over host metadata by official style guide

PR Close #26372

aio/content/examples/testing/src/testing/router-link-directive-stub.ts

@@ -1,4 +1,4 @@
-import { Directive, Input } from '@angular/core';
+import { Directive, Input, HostListener } from '@angular/core';
 
 // export for convenience.
 export { RouterLink} from '@angular/router';
@@ -6,13 +6,13 @@ export { RouterLink} from '@angular/router';
 /* tslint:disable:directive-class-suffix */
 // #docregion router-link
 @Directive({
-  selector: '[routerLink]',
-  host: { '(click)': 'onClick()' }
+  selector: '[routerLink]'
 })
 export class RouterLinkDirectiveStub {
   @Input('routerLink') linkParams: any;
   navigatedTo: any = null;
 
+  @HostListener('click')
   onClick() {
     this.navigatedTo = this.linkParams;
   }