FirebaseError when using fakeAsync

I'm seeing `Firebase: Error (auth/network-request-failed)` when using `fakeAsync`, but success without using it. (While using the emulator on localhost during test runs.)

```ts
it('should recover email fakeAsync', fakeAsync((): void => {
console.log('START');
service.recoverEmail$(testOobCode).subscribe({
error: fail,
next: (data: RecoverEmailResults): void => {
expect(data).withContext('RecoverEmailResults').toEqual({
passwordResetSent: true,
restoredEmail: testOriginalEmail,
successful: true,
});
},
});

tick(600);
flush(); // Makes the promises actually settle within the test lifetime.
console.log('END');
}));
```
`recoverEmail$` is calling `checkActionCode` (and `applyActionCode`, but it doesn't get there) from Firebase. (`@angular/fire/auth` wrappers, current 19.0.0 version). Best I can tell firebase just uses browser `fetch`, but I cannot find any reports of problems with `fakeAsync` and `fetch` (possibly due to the commonness of the word `fetch` in code discussions).

Full code is here: https://github.com/rgant/brainfry/tree/main/src/app/identity/recover-email

从提供的 recover-email 代码及其 fakeAsync 测试开始，然后检查 localhost 模拟器运行时 recoverEmail$ 如何到达 Firebase Auth checkActionCode。使用 tick(600) 和 flush(); 重现该失败；完成意味着测试在 fakeAsync 下成功完成，且没有出现 auth/network-request-failed。

由索引模型根据 Issue 内容生成。