Fix dask-core pinning to properly exclude nightlies

[charlesbluca]

As brought up in conda-forge/dask-feedstock#190 (comment), the pinning introduced in #217 accidentally blocked the security backport proposal - tested this new pinning out locally and it seems to work with backports while also blocking nightly packages.

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[charlesbluca]

@conda-forge-admin, please rerender

[github-actions]

Hi! This is the friendly automated conda-forge-webservice.

I tried to rerender for you, but it looks like there was nothing to do.

This message was generated by GitHub actions workflow run https://github.com/conda-forge/distributed-feedstock/actions/runs/2868264018.

[jrbourbeau]

Thanks @charlesbluca! Seems reasonable to me -- @jakirkham do you have a minute to look at this?

[jrbourbeau]

Thanks @charlesbluca -- will plan to merge this at EOD if no further comments

[jakirkham]

Have the same feedback as in the other review ( conda-forge/dask-feedstock#191 (review) ). Would suggest we keep this discussion in that thread for now and then apply whatever we decide to both PRs

[jakirkham]

@jrbourbeau, could you please take a look at this as well?

If this seems reasonable, would like to merge it before we merge the release PR. That way the new release will have the right version constraint to start 🙂