style(docs-infra): fix docs examples for tslint rule `import-spacing` (#38143)

This commit updates the docs examples to be compatible with the
`import-spacing` tslint rule.

This is in preparation of updating the docs examples `tslint.json` to
match the one generated for new Angular CLI apps in a future commit.

PR Close #38143

aio/content/examples/ngmodules/src/app/items/items-list.component.ts

@@ -1,8 +1,7 @@
 import { Component, OnInit } from '@angular/core';
 import { Observable } from 'rxjs';
 
-import { Item,
-         ItemService }     from './items.service';
+import { Item, ItemService } from './items.service';
 
 @Component({
   template: `

aio/content/examples/testing/src/app/dashboard/dashboard-hero.component.spec.ts

@@ -1,7 +1,6 @@
 
 // #docplaster
-import { async, ComponentFixture, TestBed
-} from '@angular/core/testing';
+import { async, ComponentFixture, TestBed } from '@angular/core/testing';
 
 import { By } from '@angular/platform-browser';
 import { DebugElement } from '@angular/core';