Beacon beam texture is stretched

The bug

The pixels on the beacon beam are not perfect squares, and are instead stretched into rectangles. Both the inner and outer beam are affected.

How to reproduce

1. Optionally, download the attached resource pack
2. Optionally, use the tick freeze command to stop the beam rotating/animating
3. Observe the beam up close

Expected results

Square pixels.

Actual results

Irregular rectangles.