Test benchmark data for the doublet GHA

[sjspielman]

If you have a small dataset that you can download and run instead, that would be the preferred solution: you can set a ENV variable to select that option when running your wrapper script.

I had been wondering about this too. I think this is a separate PR, to not automatically download the full benchmark zip, but include an option to use smaller zip file with dummy data. I'd also have to change the dataset array here, too.

Originally posted by @sjspielman in #462 (comment)

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This issue tracks (maybe!) adding tests benchmark data to improve the doublet detection workflow. That said, it's worth noting that, in the end, we may not care too too much about benchmarking results vs the doublet results on ScPCA data.