[Bug] Crash on Quit when using Analytics, Crashlytics, and Remote Config

### [REQUIRED] Please fill in the following fields:

* Unity editor version: unity 2020.3.22f1 (but seems like all)
* Firebase Unity SDK version: Since 8.6.1
* Source you installed the SDK: unitypackage
* Problematic Firebase Component: Analytics, Crashlytics, and Remote Config
* Other Firebase Components in use: N/A
* Additional SDKs you are using: Unknown
* Platform you are using the Unity editor on: Mac
* Platform you are targeting: Android
* Scripting Runtime: IL2CPP
* Pre-built SDK from the [website](https://firebase.google.com/download/unity) or open-source from this repo: Prebuilt

### [REQUIRED] Please describe the issue here:

(Please list the full steps to reproduce the issue. Include device logs, Unity logs, and stack traces if available.)

#### Steps to reproduce:

One of the issues flagged in https://github.com/firebase/quickstart-unity/issues/1193#issuecomment-1036330576. It seems like there is a problem when the application is shutting down that can result in a crash. There are a variety of users with different reports, but nothing concrete on reproduction steps, but the most relevant apis are Analytics, Crashlytics, and possibly Remote Config (though it isn't always included).

A possible way to reproduce the problem is adding a call to Unity's Application.Quit(), and watching the logs to see if anything odd appears.