refactor(docs-infra): fix docs examples for tslint rules related to object properties (#38143)

This commit updates the docs examples to be compatible with the
`no-string-literal`, `object-literal-key-quotes` and
`object-literal-shorthand` tslint rules.

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/http/src/testing/http-client.spec.ts

@@ -73,7 +73,7 @@ describe('HttpClient testing', () => {
 
     // Make an HTTP GET request with specific header
     httpClient.get<Data>(testUrl, {
-        headers: new HttpHeaders({'Authorization': 'my-auth-token'})
+        headers: new HttpHeaders({Authorization: 'my-auth-token'})
       })
       .subscribe(data =>
         expect(data).toEqual(testData)