fix if statment

Author: amitgilad3

pyiceberg/table/inspect.py

@@ -722,7 +722,7 @@ def position_deletes(self, snapshot_id: Optional[int] = None) -> "pa.Table":
             schema = self._get_positional_deletes_schema()
             return pa.Table.from_pylist([], schema=schema)
 
-        if snapshot.schema_id == None:
+        if snapshot.schema_id is None:
             raise ValueError(f"Snapshot {snapshot.snapshot_id} does not have a schema id")
 
         schemas = self.tbl.schemas()