Pin dill lower version
Pin `dill` lower version compatible with `datasets`.

Related to:
- #5487
- #288

Note that the required `dill._dill` module was introduced in dill-2.8.0, however we have heuristically tested that datasets can only be installed with dill>=3.0.0 (otherwise pip hangs indefinitely while preparing metadata for multiprocess-0.70.7)
