pin mujoco <= 3.1.1

pyproject.toml

@@ -41,7 +41,7 @@ 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 = ["mujoco >=2.1.5", "imageio >=2.14.1"]
+mujoco = ["mujoco >=2.1.5, <= 3.1.1", "imageio >=2.14.1"]
 toy-text = ["pygame >=2.1.3"]
 toy_text = ["pygame >=2.1.3"]         # kept for backward compatibility
 jax = ["jax >=0.4.0", "jaxlib >=0.4.0", "flax >= 0.5.0"]
@@ -67,7 +67,7 @@ all = [
     "mujoco-py >=2.1,<2.2",
     "cython<3",
     # mujoco
-    "mujoco >=2.1.5",
+    "mujoco >=2.1.5, <=3.1.1",
     "imageio >=2.14.1",
     # toy-text
     "pygame >=2.1.3",