Use subtreeangmom sensor instead of subtreelinvel

[miguel131299]

A subtreelinvel was mistakenly being used instead of the subtreeangmom as the name of the sensor would sugest

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[thowell]

LGTM

[yuvaltassa]

Unclear why the tests are failing...
@nimrod-gileadi @thowell @erez-tom any ideas?

[nimrod-gileadi]

The build was failing in MuJoCo. I think this was the failure that was introduced by google-deepmind/mujoco@5fcdae7 and fixed by google-deepmind/mujoco@7603b07.

If we rerun the tests now against the latest MuJoCo I expect they'll pass.

[thowell]

@miguel131299 can you please update this PR (use an empty commit so the tests are rerun), then we can merge.