A friend of mine pointed to me that the texture pack "3.0.3 Visual Enchantments" https://www.curseforge.com/minecraft/texture-packs/visual-enchantments has 3d tridents, I know the issue was just fixed for the textures, tought I'd point out this too, btw thanks a lot for fixing the texture issue :D

Trident models are not items but are actually using entity renderers. If you open up the pack you can see that they are using CEM/Random Entities and not CIT.

There are (quite far away) plans to have a way to change the trident but that's not an option now.
You'll have to find another mod to do that.