32845.Enhancement - Scikit Learn

:class:linear_model.ElasticNet, :class:linear_model.ElasticNetCV and :func:linear_model.enet_path now are able to fit Ridge regression, i.e. setting l1_ratio=0. Before this PR, the stopping criterion was a formulation of the dual gap that breaks down for l1_ratio=0. Now, an alternative dual gap formulation is used for this setting. This reduces the noise of raised warnings. By :user:Christian Lorentzen <lorentzenchr>.