fix(sumstats): correct study id for dir of finngen studies

[louwenjjr]

✨ Context

When input is a directory the study ids are not read correctly for finngen sumstats.

🛠 What does this PR implement

Extract finngen study_id by using f.input_file_name() instead of study_id = raw_file.split("/")[-1].split(".")[0].upper().

🙈 Missing

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[ireneisdoomed]

This is a better approach and the pattern works as expected. Thank you for the contribution!!

(The harmonisation of all Finngen summary statistics is particularly tricky. The DAG currently sends one job per study, any optimisations here are welcome)

Please, update the branch with base.