There is a new release of league/oauth2-client that brings a breaking change for this package.

The method League\OAuth2\Client\Provider\AbstractProvider::getResourceOwnerDetailsUrl was updated by changing its argument type from League\OAuth2\Client\Token\AccessToken to League\OAuth2\Client\Token\AccessTokenInterface.
This breaks the class inheritance for Omines\OAuth2\Client\Provider\GitLab::getResourceOwnerDetailsUrl