make subtype as required parameter

Author: adi611

pydra/engine/workers.py

@@ -893,7 +893,7 @@ def close(self):
 
 
 class PsijWorker(Worker):
-    def __init__(self, subtype=None, **kwargs):
+    def __init__(self, subtype, **kwargs):
         """Initialize worker."""
         try:
             import psij