Update pyiceberg/expressions/__init__.py

Co-authored-by: Fokko Driesprong <fokko@apache.org>

Author: Aniketsy

pyiceberg/expressions/__init__.py

@@ -685,7 +685,7 @@ def as_unbound(self) -> Type[NotIn[L]]:
 
 
 class In(SetPredicate[L]):
-    type: str = Field(default="in", alias="type")
+    type: Literal["in"] = Field(default="in", alias="type")
 
     def __new__(  # type: ignore  # pylint: disable=W0221
         cls, term: Union[str, UnboundTerm[Any]], literals: Union[Iterable[L], Iterable[Literal[L]]]