Pin orbax-checkpoint to 0.11.23 to avoid compatibility issue with jax==0.5.3

[cmj2002]

This PR addresses a dependency conflict that can occur when users have jax==0.5.3 installed and do not specify an upper bound for the orbax-checkpoint dependency.

The issue is as follows:

1. flow-rl currently requires jax==0.5.3 and does not specify an upper bound for the orbax-checkpoint dependency.
2. orbax-checkpoint version 0.11.24 introduced a call to jax.monitoring.record_scalar, which only exists in jax>=0.6.0.
3. orbax-checkpoint version 0.11.24 did not enforce a jax>=0.6.0 dependency, allowing it to be installed alongside jax==0.5.3.
4. Although orbax-checkpoint version 0.11.25 corrected this by adding the jax>=0.6.0 requirement, version 0.11.24 remains available on PyPI, leading to installation and runtime failures for users with the current dependency setup of flow-rl.

Solution: This PR pins the orbax-checkpoint dependency to 0.11.23, the newest version which does not require jax>=0.6.0.

[typoverflow]

Is it possible for us to upgrade our jax version to >= 0.6.0?