auth emulator for extensions doesn't run

### [REQUIRED] Environment info

**firebase-tools:**
8.17.0

**Platform:**
macOS Catalina 10.15.4

### [REQUIRED] Test case

See steps to reproduce.

### [REQUIRED] Steps to reproduce

1. git clone `git@github.com:firebase/extensions.git`
2. run `npm i` from root of extension's directory.
3. cd `delete-user-data` directory
4. create `test-params.env` file. Add environment variables & insert project id as appropriate:
```env
LOCATION=europe-west2
STORAGE_PATHS={DEFAULT}/test/{UID}-test.png
SELECTED_DATABASE_INSTANCE=[INSERT YOUR OWN PROJECT ID]
FIRESTORE_DELETE_MODE=shallow
```
5. delete line 159: `default: ${DATABASE_INSTANCE}` & `validationRegex: ^([0-9a-z_.-]*)$` from the `extension.yaml` file otherwise you will encounter the issue I raised [here](https://github.com/firebase/firebase-tools/issues/2928).
6. run CLI command with your project id : `firebase ext:dev:emulators:start --test-params=test-params.env --project=[INSERT YOUR OWN PROJECT ID]`

### [REQUIRED] Expected behavior

I expect to have Cloud Function and Auth emulators running.

### [REQUIRED] Actual behavior

The auth emulator does not run: