Create automated GHA tests for ecosystem projects

[dholth]

Checklist

• [X] I added a descriptive title
• [X] I searched open reports and couldn't find a duplicate

What happened?

Changes in conda break packages that use conda.

Following the model of https://github.com/conda/conda-index/pull/99, create GitHub actions jobs that run client test suites on a [weekly] schedule in packages like conda-build, conda-lock, conda-libmamba-solver? etc.

Then we can check those tests before releasing the next conda, correcting conda regressions as necessary.

For extra credit, have them post failures to a centralized channel.

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Thanks!