[dask][gpu] Run Dask tests with LightGBM GPU version

[jgiannuzzi]

As it was suggested in https://github.com/microsoft/LightGBM/pull/5282#issue-1268671683 (previous attempt: #5285).

Using findings from https://github.com/microsoft/LightGBM/pull/5282#issuecomment-1155440483:

My understanding is that the dask tests only fail with this error on Ubuntu 14.04 with Python 3.10. I ran them locally with Python 3.8 and 3.9 and they work fine. Do we maybe want to set PYTHON_VERSION again on the Linux gpu_source job?

On Ubuntu 20.04, the tests seem to fail because of a timeout. Enabling those tests on a fake GPU is expected to take more time. Maybe setting timeoutInMinutes like we do for the aarch64 job would help?