Cannot run JUnit tests

[mezz]

This might be a bug, or it might be user error, I am not sure.
I couldn't find the right way to run JUnit tests with NeoGradle.

Previously, I had a hack in my gradle code that allowed them to run, but I had to remove it in order to publish non-fat jars to maven.
mezz/JustEnoughItems@e74e8e2#diff-17b5346b7751d307bcff68a78a64a459432c4fea0cad7f58903e6e8cee8c21d8L58-L71

Without that, I run into an issue when running ./gradlew :NeoForge:test:

Caused by: net.neoforged.fml.ModLoadingException: Loading errors encountered:
    - Just Enough Items (jei) encountered an error while dispatching the net.neoforged.neoforge.network.event.RegisterPayloadHandlersEvent event
      java.lang.LinkageError: loader constraint violation: loader 'app' wants to load class net.minecraft.server.level.ServerPlayer. A different class with the same name was previously loaded by 'TRANSFORMER' @4a058df8. (net.minecraft.server.level.ServerPlayer is in module [email protected] of loader 'TRANSFORMER' @4a058df8, parent loader 'bootstrap')

longer log: https://gist.github.com/mezz/cf261ae3a0e25246c727740fc03227b8