[Ray] Enable CI of mars/learn for Ray DAG

[fyrestone]

What do these changes do?

Enables CI of mars/learn for Ray DAG.

• Fix Ray executor failed to run learn shuffle.
• Fix Ray executor shuffle colouring bug.
• Fix Ray executor raises KeyError when exiting stage.
• Fix Ray executor raises ValueError when running learn LabelEncoder.
• Fix Ray executor raises ValueError: WRITEBACKIFCOPY base is read-only.
• Fix Ray executor raises ValueError: Tileable object must be executed first before fetch.
• Fix ParallelPostFit raises AttributeError: 'GradientBoostingClassifier' object has no attribute '_loss'.

Related issue number

Fixes: https://github.com/mars-project/mars/issues/3260 https://github.com/mars-project/mars/issues/3262 https://github.com/mars-project/mars/issues/3267 https://github.com/mars-project/mars/issues/3268 https://github.com/mars-project/mars/issues/3269 https://github.com/mars-project/mars/issues/3266 https://github.com/mars-project/mars/issues/3270

Related: https://github.com/mars-project/mars/pull/3239

Check code requirements

• [ ] tests added / passed (if needed)
• [ ] Ensure all linting tests pass, see here for how to run them