Unhelpful/Misleading Error Message when Credentials File is Empty

#### Environment details

- OS: Alpine
- Node.js version: 18.12.0
- npm version: 8.19.2
- `@googleapis/google-auth-library-nodejs` version: 8.7.0

#### Steps to reproduce

1. Create an empty `gcp_credentials.json` file for your `gcloud_project` with your `gcloud_storage_bucket`.
2. Use, e.g.:

```
const storage = new Storage({
projectId: gcloud_project,
keyFilename: 'gcp_credentials.json'
});

const bucket = storage.bucket(gcloud_storage_bucket);
const [metadata] = await bucket.getMetadata();
```

3. Receive unhelpful error message "TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type boolean (true)"

It would be reasonable to sanity-check the key file and return a more illuminating error message.