[ci] migrate CI from macOS 10.15 to 11 (fixes #5391)

[StrikerRUS]

Closed #5391.

[StrikerRUS]

Seems that #5390 blocks this PR.

PackagesNotFoundError: The following packages are not available from current channels:

  - dask=2022.7.0
  - distributed=2022.7.0

Current channels:

  - https://conda.anaconda.org/conda-forge/osx-64
  - https://conda.anaconda.org/conda-forge/noarch

[jameslamb]

I just took over this PR. We only have 10 more days to apply this change, before macOS jobs start failing on Azure DevOps.

Given that, I'm proposing the following additional changes to what @StrikerRUS originally had here:

• skip the one test that fails on newer dask / distributed (and keep [ci] [dask] CI jobs failing with Dask 2022.7.1 #5390 open to track the work of reinstating that task)
• remove the pin on dask / distributed versions in CI
• switch from installing dask to installing dask-core in CI
  • dask-core is like dask, but without dependencies like bokeh that are intended for interactive use and not necessary for LightGBM's CI

@jmoralez @guolinke the next time you have a few minutes to review a PR in this repo, will you please review this one?

[jameslamb]

Thanks so much for doing this @StrikerRUS , especially for your expertise around how the XCode version relates to the way the wheels are tagged!

[github-actions]

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