Add missing gain type "affine" to general actuators.
Add missing gain type "affine" to general actuators.

PiperOrigin-RevId: 463605415
Change-Id: I849e6f2f0ec5eaedaa774099e5e07f27919bb943

deepmind/mujoco,deepmind/mujoco,deepmind/mujoco,deepmind/mujoco,deepmind/mujoco