Redmine

The attached patch fix-2fa-argument-error.patch fixes the error described below. The error occurs in development mode. No problem in production mode.

Steps to reproduce:

1. Run Redmine in development mode (bin/rails s)
2. Login with any user
3. Go to "My account" and click "Enable authenticator app"
4. Setup up two-factor authentication for the account
5. Update some source file of Redmine (e.g. run touch config/locales/en.yml)
6. 2. Go to "My account" and click "Generate backup codes"
7. You will see the following error entering your authentication code

ArgumentError in TwofaBackupCodesController#create
A copy of Redmine::Twofa::Base has been removed from the module tree but is still active!