Why 5.Bg5? I don't feel like it's very challenging. You can just do Bg2, since you've committed to that already, and ...h6 is a waste of time for black. The whole variation doesn't seem to give white anything, and black is totally fine afterwards.
Then after 5.Bg2 if black plays something like 5...Nbd7 6.0-0 Bd6 then 7.Nfd2! is very effective, giving white a nice opening edge. So usually black plays 6...Bb4+.
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