It's a thin walled aluminum tube, the crack will propagate. There are no plugs or fillers or sleeves that will prevent that crack from propagating. You may be able to prevent a catastrophic failure at that location, but the crack will spread and the top tube will crack elsewhere.

I strongly suggest you stop riding that frame, but if you refuse to yield to common sense at least keep a close watch on that area while you're riding. You might get some sort of hints just before eminent failure like rapidly spreading crack, or even creaking sounds.