env.render_mode attribute missing

[jonasreiher]

Describe the bug

The environments created via env = gym.make('PandaPush-v3', render_mode='rgb_array') (also with 'human') are missing the render_mode attribute, so env.render_mode returns None.

This attribute is required e.g. by gymnasium's PixelObservationWrapper.

To Reproduce

import gymnasium as gym
from gymnasium.wrappers import PixelObservationWrapper
import panda_gym

env = gym.make('PandaPush-v3', render_mode='rgb_array')
env = PixelObservationWrapper(env)

AttributeError: env.render_mode must be specified to use PixelObservationWrapper:`gymnasium.make(env_name, render_mode='rgb_array')`.

System

• OS: Ubuntu 20.04.5 LTS
• Python version (python --version): 3.8.10
• Package version (pip list | grep panda-gym): 3.0.3

[qgallouedec]

Also addressed in #56