Raise warning in `PixelObservationWrapper` if `render_mode` is None (#2978)
Raise warning in `PixelObservationWrapper` if `render_mode` is None (#2978)

* init

* adapt PixelObservationWrapper to new API

* reformat

Co-authored-by: younik <7fce1f85f8d8683a3e5e7a2068d984a3da2b3c3f@gmail.com>
Farama-Foundation/Gymnasium,Farama-Foundation/Gymnasium