fix MujocoPyEnv human render not being freed upon close()

[Kallinteris-Andreas]

Description

Fixes # #743

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[pseudo-rnd-thoughts]

@Kallinteris-Andreas Any progress on this?

[Kallinteris-Andreas]

Does not solve the issue

fails this test:

import pytest
import gymnasium as gym
#envs_list = list(gym.registry.keys())
#envs_list = ["Reacher-v2"]
#envs_list = ["Reacher-v2", "Ant-v3"]
envs_list = ["Reacher-v2", "Ant-v5", "Pusher-v2"]



def random_action_on_env(env_name):
    env = gym.make(env_name, render_mode="human")
    observation, info = env.reset()
    for _ in range(100):
        action = env.action_space.sample()  # agent policy that uses the observation and info
        observation, reward, terminated, truncated, info = env.step(action)

        if terminated or truncated:
            observation, info = env.reset()

    env.close()


@pytest.mark.parametrize("env_name", envs_list)
def test_random_actions(env_name):
    """random action on every env"""
    random_action_on_env(env_name)