Wallet payment source FK targets `spree_users` after user class change

Solidus Version:
2.10.2

To Reproduce

1. After installing Solidus, run db:seed to get the default values installed and add a sample product to the store.
2. Add the solidus_auth_devise gem and follow the instructions for setting Spree.user_class here: https://guides.solidus.io/developers/users/custom-authentication.html
3. Drop the spree_users table from the DB since you'll be using your existing User class.
4. Login with a test user, add the sample product to your cart and begin the checkout process. At the confirmation page, click 'Place Order' and you'll be presented with a SQLException: no such table: main.spree_users error.

Current behavior
The order should be completed successfully. Instead, an SQLException: no such table: main.spree_users error is thrown.

Expected behavior
The user should be able to successfully checkout / purchase their cart items.

Desktop (please complete the following information):

• OS: MacOS Catalina 10.15.6
• Chrome
• Version 84.0.4147.105

Additional context
Log output is available here: https://gist.github.com/paulsingh/ab49d1977219971f72430351ffecc875

Reproduce the issue by running db:seed, configuring solidus_auth_devise with a custom Spree.user_class, removing spree_users, and placing an order through checkout. Inspect the linked log and trace the wallet payment source foreign key that still targets spree_users; done means checkout completes successfully without that table.