sendEmailVerification() - Cannot assign to read only property '_canInitEmulator

Hi, I've spent so much time without finding the answer so I assume it could be a bug.
After creation of a new user by createUserWithEmailAndPassword() I'm calling current user from AngularFireAuth instance. Then I call sendEmailVerification() which causes an error:
```
TypeError: Cannot assign to read only property '_canInitEmulator' of object '[object Object]'
at index-839de510.js:937
at Generator.next ()
at asyncGeneratorStep (asyncToGenerator.js:3)
at _next (asyncToGenerator.js:25)
at asyncToGenerator.js:32
at new ZoneAwarePromise (zone.js:1387)
at asyncToGenerator.js:21
at _performFetchWithErrorHandling (index-839de510.js:936)
at index-839de510.js:913
at Generator.next ()
```
It happens for angular 12 and 13.
Angular: 13.1.0
Firebase: 9.4.0
Angularfire: 7.2.0

首先通过 AngularFireAuth 复现该流程：使用 Angular 13.1.0、Firebase 9.4.0 和 AngularFire 7.2.0 调用 createUserWithEmailAndPassword()，然后调用 sendEmailVerification()。检查经过 _performFetchWithErrorHandling 的堆栈跟踪路径；当电子邮件验证在没有只读 _canInitEmulator 错误的情况下完成时，即表示完成。

由索引模型根据 Issue 内容生成。