[RLlib] Callbacks class input check is invalid for new api stack

[n30111]

What happened + What you expected to happen

For the new api stack, callback class can be a list of callbacks, but there is validation check in the code that does not allow user to pass a list. Disabling the check for the new api stack will resolve the issue.

https://github.com/ray-project/ray/blob/master/rllib/algorithms/algorithm_config.py#L2421
Incorrect validation: https://github.com/ray-project/ray/blob/master/rllib/algorithms/algorithm_config.py#L2518

Versions / Dependencies

Master branch, python3.10 linux

Reproduction script

N/A

Issue Severity

High: It blocks me from completing my task.