use conda forge explicitly in conda build test

[pmeier]

What does this implement/fix?

This PR adds --channel=conda-forge explicitly to the conda build we are running as part of our tests. Right now our CI relies on this being set in the conda configuration file:

nebari/.github/workflows/test.yaml

Line 52 in 6b38c8c

channels: conda-forge

However, we cannot depend on this being the case locally for all other devs as well. Without setting the channel explicitly, conda build will try to pull from the defaults channel and fail, since it doesn't contain everything we need.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

• Did you test the pull request locally?
• Did you add new tests?

[trallard]

@dharhas I think I found the culprit of the conda build issue we encountered during the sprints

In hindsight, I wonder if this test needs to be run at all times or only during a pre-build/pre-packaging stage

[costrouc]

Yeah and we should be using conda-forge by default anyways. Thanks @pmeier