Fix path in "Node is dir" error message

The error message currently displays the path to the source file of the task.
This fixes it to be the path of the node being considered.

Author: egerlach

src/_pytask/collect.py

@@ -444,7 +444,7 @@ def pytask_collect_node(session: Session, path: Path, node_info: NodeInfo) -> PN
         name = shorten_path(node, session.config["paths"] or (session.config["root"],))
 
         if isinstance(node, Path) and node.is_dir():
-            raise ValueError(_TEMPLATE_ERROR_DIRECTORY.format(path=path))
+            raise ValueError(_TEMPLATE_ERROR_DIRECTORY.format(path=node))
 
         return PathNode(name=name, path=node)