/enchant cannot add enchantments that are not compatible with the item.

Steps to Reproduce:
Give yourself a trident
Use /enchant to attempt to enchant it with looting
Expected Result:
The trident should receive looting and the command is successful, similar to how tridents can be combined with a looting 3 book on an anvil
Observed result:
The trident fails to receive looting, with an error message