Fix ET1 Y-arm azimuth angle

The ET1 detector was incorrectly assigned arms with 90 degree vertex. The X-arm was consistent with the ET2 and ET3 detectors (rotated by 120 degrees) but the Y-arm was incorrect. The correct value for this should be 5.575150608203195

Cross-check: From the proposed new y-arm azimuth, add 60 degrees and confirm that this is equal to the x-arm aximuth.

>>> math.fmod(5.575150608203195 + (2*pi/6), 2*pi)
0.33916285222020637