Animating HDRI rotation should work, just don't forget that you also need to enable motion blur, but honestly, i would simply replace the background image with sky that has already star trails in it and wouldn't bother to do this in 3D. From perspective of observer on earth, stars are indistinguishable from 2D projection, you won't gain anything by rendering their motion in 3D, but you will have to pay a performance penalty.