Skip nexus test under Java test server

Author: dandavison

tests/worker/test_worker.py

@@ -445,6 +445,9 @@ def my_signal(self, value: str) -> None:
 
 
 async def test_custom_slot_supplier(client: Client, env: WorkflowEnvironment):
+    if env.supports_time_skipping:
+        pytest.skip("Nexus tests don't work under Java test server")
+
     class MyPermit(SlotPermit):
         def __init__(self, pnum: int):
             super().__init__()