This affect all local lights (non-sun light).
We hide the artifact caused by different tracing results from
two adjacent projection. This is visible as the shading point
switches projections.
We fix this by randomizing which shadow map projection (face)
to trace. We do that by using the point at half the ray instead
of the shading point to choose the projection. This gives
a soft enough look proportional to the light shape.
This also has the benefit of being stupidly simple.
Pull Request: https://projects.blender.org/blender/blender/pulls/119555
38b180f236