What should I do to fix the black line on the top of the mesh that used alpha?

Godot Version



Hello everyone, I am currently learning and trying to create a 3d-2d scene in Godot, but I have discovered a strange issue. I have made a portion of the image transparent in this image, and I am confident that the top of the image is completely blank. But in the engine, it generates a thin line at the top and can be seen both near and far, just like forgetting to clear a part of my image; How can I eliminate it?

By the way, I found that this issue seems to only occur on very large textures that use alpha. Alpha scissors do not have this problem, but it is very ugly. Even if aa is turned on, it cannot save it x(