DOC: Description and workaround of Spyder UMR conflict in known_issues

[pllim]

Fix #7363

Close #7374

This is basically the same as #7374 but it is opened against v2.0.x branch instead of master. I tried cherry-picking but that didn't work. I also didn't want to clobber @dhomeier 's branch although theoretically I could.

[astropy-bot]

Hi there @pllim 👋 - thanks for the pull request! I'm just a friendly 🤖 that checks for issues related to the changelog and making sure that this pull request is milestoned and labeled correctly. This is mainly intended for the maintainers, so if you are not a maintainer you can ignore this, and a maintainer will let you know if any action is required on your part 😃.

Everything looks good from my point of view! 👍

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[pllim]

Huh... CircleCI failed with the following error. Can anyone try to have it to pip install future to fix that error? Or can we ignore it?

Traceback (most recent call last):
  File "setup.py", line 7, in <module>
    from astropy_helpers.setup_helpers import register_commands, get_package_info
  File "/root/project/astropy_helpers/astropy_helpers/__init__.py", line 46, in <module>
    import builtins
ImportError: No module named builtins

[pllim]

FWIW I don't think the failures are related to this PR. Perhaps they are fixed in master but just not backported yet. 🤷‍♀️

[pllim]

Looking at spyder-ide/spyder#6962, it seems that this is being addressed over there, so I am closing this without merge.