docs: fix interval type in the example (#43042)

`window.setInterval` returns a `number`, let's fix this example.

PR Close #43042

aio/content/examples/dynamic-component-loader/src/app/ad-banner.component.ts

@@ -21,7 +21,7 @@ export class AdBannerComponent implements OnInit, OnDestroy {
   @Input() ads: AdItem[] = [];
   currentAdIndex = -1;
   @ViewChild(AdDirective, {static: true}) adHost!: AdDirective;
-  interval: any;
+  interval: number | undefined;
 
   constructor(private componentFactoryResolver: ComponentFactoryResolver) { }