Mark ipykernel 6.18.0 as broken

[martinRenou]

Guidelines for marking packages as broken:

• We prefer to patch the repo data (see here)
  instead of marking packages as broken. This alternative workflow makes environments more reproducible.
• Packages with requirements/metadata that are too strict but otherwise work are
  not technically broken and should not be marked as such.
• Packages with missing metadata can be marked as broken on a temporary basis
  but should be patched in the repo data and be marked unbroken later.
• In some cases where the number of users of a package is small or it is used by
  the maintainers only, we can allow packages to be marked broken more liberally.
• We (conda-forge/core) try to make a decision on these requests within 24 hours.

What will happen when a package is marked broken?

• Our bots will add the broken label to the package. The main label will remain on the package and this is normal.
• Our bots will rebuild our repodata patches to remove this package from the repodata.
• In a few hours after the anaconda.org CDN picks up the new patches, you will no longer be able to install the package from the main channel.

Checklist:

• Make sure your package is in the right spot (broken/* for adding the
  broken label, not_broken/* for removing the broken label, or token_reset/*
  for token resets)
• Added a description of the problem with the package in the PR description.
• Added links to any relevant issues/PRs in the PR description.
• Pinged the team for the package for their input.

The latest ipykernel release was yanked from Pypi https://pypi.org/project/ipykernel but it has been released on conda-forge anyway

See ipython/ipykernel#1026 (comment)

[martinRenou]

cc. @blink1073

[blink1073]

Thanks!