[Security] User refreshment from identical users provider type

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

When we are using two privoders with the same supported class but with different users, there is a faill because the first `UsernameNotFoundException` will stop the refresh processus.
"is it ok to log information about not found user even if he exists in at least one user provider?"
Yes, I did this. Each time there is a UsernameNotFoundException exception, it's because a user provider is able to load the user, but the user is not found inside this provider.

"Maybe this should be logged just before end of the method, when you're quite sure that there is no existing user"
Yes I can do that, good idea :)