replace type and __type__ in type error (#1035)

Signed-off-by: Yotam Perlitz <yotam.perlitz@ibm.com>
Signed-off-by: Benjamin Sznajder <benjams@il.ibm.com>

src/unitxt/artifact.py

@@ -124,7 +124,7 @@ def __init__(self, type) -> None:
 class MissingArtifactTypeError(ValueError):
     def __init__(self, dic) -> None:
         message = (
-            f"Missing 'type' parameter. Expected 'type' in artifact dict, got {dic}"
+            f"Missing '__type__' parameter. Expected 'type' in artifact dict, got {dic}"
         )
         super().__init__(message)