"Auth plugin not supported here" on user upload

[OxyOCE]

When uploading users via csv, if auth method is set to oidc the uploader receives the warning "Auth plugin not supported here". This doesn't affect the outcome of the upload, therefore the warning is misleading.

The fix for this issue: #2495 will also allow OIDC to be selected as a default if the auth method is not included in the csv.

Previous examples of this issue are discussed here: MDL-59306