Cannot log in to Admin API when no NativeAuthStrategy on Shop API

[michaelbromley]

Describe the bug
When the Shop API is configured to not include the NativeAuthStrategy, login with native auth is no longer possible on the Admin API.

To Reproduce
Repo here: https://github.com/codyseumWeb3/broken-admin-auth

Expected behavior
The config of the shop api should not influence the admin api auth.

Environment (please complete the following information):

• @vendure/core version: 2.0.3
• Nodejs version: any
• Database (mysql/postgres etc): any