new subworkflow: gff3_gt_gff3_gff3validator_stat

[GallVp]

Is there an existing subworkflow for this?

• [X] I have searched for the existing subworkflow

Is there an open PR for this?

• [X] I have searched for existing PRs

Is there an open issue for this?

• [X] I have searched for existing issues

Are you going to work on this?

• [X] If I'm planning to work on this subworkflow, I added myself to the Assignees to facilitate tracking who is working on the subworkflow