Apply suggestions from code review

Co-authored-by: Ralf Grubenmann <ralf.grubenmann@sdsc.ethz.ch>

renku/core/commands/workflow.py

@@ -462,14 +462,14 @@ def execute_workflow(
     """Execute a Run with/without subprocesses."""
     client = client_dispatcher.current_client
 
-    inputs = [i.actual_value for p in dag.nodes for i in p.inputs]
+    inputs = {i.actual_value for p in dag.nodes for i in p.inputs}
     # NOTE: Pull inputs from Git LFS or other storage backends
     if client.check_external_storage():
         client.pull_paths_from_storage(*inputs)
 
     # check whether the none generated inputs of workflows are available
-    outputs = set([o.actual_value for p in dag.nodes for o in p.outputs])
-    for i in set(inputs) - outputs:
+    outputs = {o.actual_value for p in dag.nodes for o in p.outputs}
+    for i in inputs - outputs:
         if not Path(i).exists():
             raise errors.ParameterError(f"Input '{i}' for the workflow does not exists!")