test(docs-infra): add unit tests for rxjs examples (#34190)

This commit adds missing unit tests for all rxjs examples from the docs.

Closes #28017

PR Close #34190

aio/content/examples/observables-in-angular/src/main.ts

@@ -1,3 +1,4 @@
+// TODO: Add unit tests for this file.
 // tslint:disable: no-output-native
 // #docregion
 import { Component, Output, OnInit, EventEmitter, NgModule } from '@angular/core';