[mujoco-playground] Allow dm_control suite tasks which use spec to construct the model to be backwards compatible with MuJoCo versions < 3.3.0.

PiperOrigin-RevId: 734620916
Change-Id: I0bb5181badbe0e1f433b3cb8870643f9c225d1ea

Author: kevinzakka

mujoco_playground/_src/dm_control_suite/reacher.py

@@ -44,7 +44,10 @@ def default_config() -> config_dict.ConfigDict:
 
 def _make_model(xml_path: epath.Path, target_size: float) -> mujoco.MjModel:
   spec = mujoco.MjSpec.from_string(xml_path.read_text(), common.get_assets())
-  target_body = spec.body("target")
+  if mujoco.__version__ >= "3.3.0":
+    target_body = spec.body("target")
+  else:
+    target_body = spec.find_body("target")
   target_geom = target_body.first_geom()
   target_geom.size[0] = target_size
   return spec.compile()