Follow up from #3705 (comment)

We would like to cleanup the __being_called_by_pytest keyword hack that was used in #3705. @RonnyPfannschmidt's suggestion of unwrapping the fixture function just before the call works great, except that for staticmethods we don't have access to instance request at that point.

It seems like a deeper issue in the structural construction of the request: static test functions should still have self in request.instance.