This isn't entirely Wurst-related, but since there isn't much public info about it, and search engines generally index the Wurst forum, I thought I'd write about it here. It might be useful to someone.
The test gets stuck when creating a new world due to an issue with the network synchronizer. Currently, GameTests always fail in private repos, at least in my experience. This can also happen in public repos, though it's rare, likely because public CIs have twice as many CPU cores and more RAM. I haven't looked into it much, so I'm not sure, but that's the only difference I can think of.
The simplest workaround is to add the following to the Loom run config:
vmArgs.add("-Dfabric.client.gametest.disableNetworkSynchronizer=true")
per: https://docs.fabricmc.net/develop/automatic-testing#run-game-tests-on-github-actions
