use mujoco-py-cython3 to retain compatibility

docs/environments/mujoco.md

@@ -38,7 +38,9 @@ As of October 2021, DeepMind has acquired MuJoCo and has open-sourced it in 2022
 Using MuJoCo with Gymnasium requires the framework `mujoco` be installed (this dependency is installed with the above command).
 Instructions for installing the MuJoCo engine can be found on their [website](https://mujoco.org) and [GitHub repository](https://github.com/deepmind/mujoco).
 
-For MuJoCo `v3` environments and older the `mujoco-py` framework is required (`pip install gymnasium[mujoco-py]`) which can be found in the [GitHub repository](https://github.com/openai/mujoco-py/tree/master/mujoco_py).
+For MuJoCo `v3` environments and older the `mujoco-py` framework is required
+`pip install gymnasium[mujoco-py]` installs a fork of [mujoco-py] which works with `cython>=3.0.0` otherwise `pip install gymnasium[mujoco-py-original]` installs the original
+which can be found in the [GitHub repository](https://github.com/openai/mujoco-py/tree/master/mujoco_py), but it does not work `cython>=3.0.0`.
 
 There are eleven MuJoCo environments (in roughly increasing complexity):
 

pyproject.toml

@@ -39,8 +39,9 @@ atari = ["ale_py >=0.9"]
 box2d = ["box2d-py ==2.3.5", "pygame >=2.1.3", "swig ==4.*"]
 classic-control = ["pygame >=2.1.3"]
 classic_control = ["pygame >=2.1.3"]  # kept for backward compatibility
-mujoco-py = ["mujoco-py >=2.1,<2.2", "cython<3"]
-mujoco_py = ["mujoco-py >=2.1,<2.2", "cython<3"]  # kept for backward compatibility
+mujoco-py = ["mujoco-py-cython3"]
+mujoco_py = ["mujoco-py-cython3"]  # kept for backward compatibility
+mujoco-py_original = ["mujoco-py >=2.1,<2.2", "cython<3"]
 mujoco = ["mujoco >=2.1.5", "imageio >=2.14.1", "packaging >=23.0"]
 toy-text = ["pygame >=2.1.3"]
 toy_text = ["pygame >=2.1.3"]  # kept for backward compatibility
@@ -59,8 +60,7 @@ all = [
     # classic-control
     "pygame >=2.1.3",
     # mujoco-py
-    "mujoco-py >=2.1,<2.2",
-    "cython <3",
+    "mujoco-py-cython3",
     # mujoco
     "mujoco >=2.1.5",
     "imageio >=2.14.1",