CI: Add job to validate conda-forge meta.yaml
xref https://github.com/pandas-dev/pandas/pull/52794#issuecomment-1527919521 cc @datapythonista 

Inspired by https://github.com/dask/dask/blob/main/.github/workflows/conda.yml
Going to merge this in, but happy to address any followups Thanks for this @mroeschke, looks great!