120mm fan shroud for Radeon Instinct MI25/MI50

Remix of https://www.thingiverse.com/thing:6636428 120mm fan shroud "type a": moved the GPU fixing holes down 2mm to match the GPU and reduced the fan plate from 4mm to 2mm, otherwise the screws didn't grab on the fan.

See also this design https://www.thingiverse.com/thing:7179158 for another 120mm fan shroud for MI25/MI50.