fixed the docstring to match the ErrorValue

src/sage/coding/linear_code.py

@@ -1960,7 +1960,7 @@ def __call__(self, m, **kwargs):
             sage: C(word)
             Traceback (most recent call last):
             ...
-            ValueError: If the input is a vector whose length is equal to self.length(), it has to be a codeword
+            ValueError: If the input is a vector which belongs to the ambient space, it has to be a codeword
         """
         if m in self.ambient_space() and m not in self:
             raise ValueError("If the input is a vector which belongs to the ambient space, it has to be a codeword")