Two consecutive `subscribe` calls on the Observable created by `authState()` cause Angular app to never become stable.

### Version info

**Angular:** 18.0.3

**Firebase:** 10.12.2

**AngularFire:** 18.0.1

### How to reproduce these conditions

**Failing test unit, Stackblitz demonstrating the problem**

Stackblitz example with the problem: https://stackblitz.com/edit/stackblitz-starters-zfidzt?file=src%2Fmain.ts

**Steps to set up and reproduce**

- Open Stackblitz reproduction
- Check the console, and see that the `ApplicationRef.isStable` never emits true

### Debug output

**Errors in the JavaScript console**

message: `isStable: true` is expected, but it never comes

### Expected behavior

`ApplicationRef.isStable` emits `true` after application start.
### Actual behavior

`ApplicationRef.isStable` never emits `true`, if two consecutive `subscribe` calls on the Observable created by `authState()` are made.

从链接的 StackBlitz 复现开始，尤其关注 src/main.ts，并复现对 authState() 的两次连续 subscribe 调用。观察 ApplicationRef.isStable，并将结果与应用启动后预期发出的 true 进行比较；在此复现中应用变得稳定即表示完成。

由索引模型根据 Issue 内容生成。