fix and bump gfastats

[fellen31]

PR checklist

Closes #XXX

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[fellen31]

I'm just getting empty genome.fastas in the nf-test work directories. Can you see what I'm missing here?

[mahesh-panchal]

I think change the code so that --out-format is not mandatory. The summary is the important part. I must have missed that it's optional to write out an assembly.