Piston can push NoGravity ArmorStand

Pistons can still push NoGravity armor stands, even though NoGravity should disable all physics on the stand.

To test:

1. Summon NoGravity armor stand
2. Point a piston at it
3. Power piston to see it is moved

NoGravity ArmorStands are not affected by other physics interactions (excluding being a passenger of another entity) such as explosions and water, .