Fix cast and test

Author: stefanvanburen

src/celpy/celtypes.py

@@ -443,7 +443,7 @@ def __repr__(self) -> str:
         return f"{self.__class__.__name__}({super().__repr__()})"
 
     def contains(self, item: Value) -> BoolType:
-        return BoolType(cast(StringType, item) in self)
+        return BoolType(cast(BytesType, item) in self)
 
 
 class DoubleType(float):

tests/test_celtypes.py

@@ -81,7 +81,7 @@ def test_bytes_type():
     assert repr(b_0) == "BytesType(b'bytes')"
     assert BytesType(None) == BytesType(b'')
     assert BytesType(MessageType({"value": BytesType(b'42')})) == BytesType(b'42')
-    assert b_0.contains("byte")
+    assert b_0.contains(b"byte")
 
 
 def test_double_type():