Remove duplicate colon in coercion error message

Replicates graphql/graphql-js@e919361

Author: Cito

src/graphql/utilities/coerce_input_value.py

@@ -28,7 +28,7 @@ def default_on_error(
 ) -> None:
     error_prefix = "Invalid value " + inspect(invalid_value)
     if path:
-        error_prefix += f" at 'value{print_path_list(path)}': "
+        error_prefix += f" at 'value{print_path_list(path)}'"
     error.message = error_prefix + ": " + error.message
     raise error
 

tests/utilities/test_coerce_input_value.py

@@ -338,6 +338,6 @@ def throw_error_with_path():
                     [None], GraphQLList(GraphQLNonNull(GraphQLInt))
                 )
             assert exc_info.value.message == (
-                "Invalid value None at 'value[0]': :"
+                "Invalid value None at 'value[0]':"
                 " Expected non-nullable type Int! not to be None."
             )