minor symfony#10213 [Security] Fix wrong usage in custom authenticator checking if password is invalid (norkunas)

This PR was merged into the 2.8 branch.

Discussion
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[Security] Fix wrong usage in custom authenticator checking if password is invalid

```Symfony\Component\Security\Core\Encoder\UserPasswordEncoderInterface::isPasswordValid``` expects an UserInterface and a password, but example arguments was provided like for `Symfony\Component\Security\Core\Encoder\PasswordEncoderInterface`
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Commits
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94f2951 Fix wrong usage in custom authenticator checking if password is invalid

Author: xabbuh

security/custom_password_authenticator.rst

@@ -69,7 +69,7 @@ the user::
                 if ('' === ($givenPassword = $token->getCredentials())) {
                     throw new BadCredentialsException('The given password cannot be empty.');
                 }
-                if (!$this->encoder->isPasswordValid($user->getPassword(), $givenPassword, $user->getSalt())) {
+                if (!$this->encoder->isPasswordValid($user, $givenPassword)) {
                     throw new BadCredentialsException('The given password is invalid.');
                 }
             }