Fixes Redis::Failure::RedisMultiQueue#filter_backtrace to match Redis::Failure::Redis#filter_backtrace

This is a minor fix that should have been made when `Redis::Failure::Redis#filter_backtrace` was modified. I guess it was omitted because of the high level of code duplication between `Redis::Failure::Redis` and `Redis::Failure::RedisMultiQueue`. It would be nice to refactor these.