Allow Fatal Error Assertions to Accept Expected Message as Multiple Values

[threeal]

This issue suggests modifying the MESSAGE option in the assert_fatal_error function to accept multiple values, allowing the expected message value to be separated, similar to how value in the message function can also be separated.

This change may simplify how the user calls the assert_fatal_error function, allowing the expected message, which may contain multiple lines, to be passed easily to the function without the need to create another variable just to format the expected message into several values.