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.

Reproduce the issue with Angular 12.1.1, Firebase 9.1.3, AngularFire 7.1.0, and RxJS 7.2.0 using AngularFireFunctions from @angular/fire/compat/functions. Start at httpsCallable and check how its invocation interacts with Angular Zone, including when wrapped in ngZone.runOutsideAngular. Done means callable invocations no longer leave long-lived pending tasks or make the Zone unstable.

Written by the indexing model from the issue text.