Any evocation of fireFunctions.httpsCallable make Angular Zone instable

### Version info

**Angular:**
12.1.1

**Firebase:**
9.1.3

**AngularFire:**
7.1.0

**Other (e.g. Ionic/Cordova, Node, browser, operating system):**
rxjs: 7.2.0

### How to reproduce these conditions

Any evocation of `fireFunctions.httpsCallable` make Angular Zone instable.

**Context**

In my angular application, I have a code that detects pending tasks executed inside Angular Zone. I noticed after upgrade on 7.1.0 that evocation of httpCallables leave long living tasks in the Zone. This was never an issue before. Even wrapping those calls into `ngZone.runOutsideAngular` doesn't help. Example:

```typescript
import {AngularFireFunctions} from '@angular/fire/compat/functions';
//...
constructor(private readonly fireFunctions: AngularFireFunctions) {
}

this.fireFunctions.httpsCallable('myFunc')(data); // this code creates a long living task inside zone and make it unstable

```

### Expected behavior

Evocation of httpCallable functions must not make zone unstable.

使用来自 @angular/fire/compat/functions 的 AngularFireFunctions，在 Angular 12.1.1、Firebase 9.1.3、AngularFire 7.1.0 和 RxJS 7.2.0 中复现该问题。从 httpsCallable 开始，检查其调用如何与 Angular Zone 交互，包括将其包装在 ngZone.runOutsideAngular 中时的情况。当 callable 调用不再留下长期存在的 pending task 或使 Zone 变得不稳定时，即表示完成。

由索引模型根据 Issue 内容生成。