DEBUG_MODE is false only if it is not listed in app.module.ts

### Version info

**Angular:** 12.2.0

**Firebase:** 9.6.6

**AngularFire:** 7.2.1

### How to reproduce these conditions

**Steps to set up and reproduce**

In app.module.ts:

`{ provide: DEBUG_MODE, useValue: true }`
`{ provide: DEBUG_MODE, useValue: false }`

Both two use cases listed above activate the debug mode in Firebase Console. If I omit DEBUG_MODE altogether from providers, only then does it not activate debug mode.

Start with the DEBUG_MODE provider entries in app.module.ts and trace how AngularFire passes that value to Firebase. Reproduce the behavior with DEBUG_MODE set to true, false, and omitted, then verify that false no longer activates debug mode in the Firebase Console.

Written by the indexing model from the issue text.