@ShiosakiYuta Thanks for sending the reproduction package, we received everything. It was indeed a bug which you have discovered regarding GI and slot alpha transparency, thank you for reporting!
A new 4.2 Spine URP Shaders UPM package is available for download:
https://esotericsoftware.com/spine-unity-download
Please let us know whether this resolves the issue for you as well.
Issue ticket URL for later reference:
EsotericSoftware/spine-runtimes2798
A side note: in your reproduction project, the settings of both skeleton atlas textures and materials were incorrectly set up for PMA workflow, but the textures seem to have been exported as straight alpha workflow. This leads to additional undesired light outlines around attachments. I assume that this was just the case in your reproduction project. I'm mentioning it anyway in case it is relevant for your main project.