added scvi-scarches-xgb to label projection

[LuckyMD]

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[LuckyMD]

Not sure what code version to use here... xgboost or scvi-tools. I guess mostly the latter is used... or can I quote both versions?

Also, forgot to do this on my own fork :/.

[LuckyMD]

Now also on my fork, here: LuckyMD#8

[LuckyMD]

Will redo PR from my fork