Update g1_mjx.xml right_hip_roll joint limit

[silviacruciani]

Description

Update right hip joint limit according to value in robot datasheet

This also matches the model in https://github.com/google-deepmind/mujoco_menagerie/blob/main/unitree_g1/g1.xml

Checklist

• Added your name to CONTRIBUTORS.md (alphabetically by first name)
• Updated CHANGELOG.md:
  • [N/A] Global changelog (if your change affects the overall repo)
  • Model-specific changelog (if it affects a specific model only)
• [N/A] Followed the XML formatting/style guidelines (if editing MJCF)
• Ran pytest test/ locally and ensured all tests pass
• [N/A] Signed the Contributor License Agreement (CLA)

[kevinzakka]

Thanks @silviacruciani!