dispatch: restore `--config` can't be abbreviated message in case of ambiguity This feels kind of gross, in part because it's a surprising amount of code for a specific edge case, and in part because it assumes some implementation details. But I don't see a better way, since `getopt.long_has_args()` will create a list of all known long options that start with the current option, and raise errors of this type if the list is either empty or has more than one element. There's not a programmatic way to tell the difference between these two aside from parsing the message, so we replicate the check here and raise the expected exception in the case of ambiguity. Otherwise, the original expection is re-raised.