Raytraced lights with Source Length > 0 behave incorrectly with Megalights

When Megalights is enabled, light can leak into areas that should be occluded for lights with smallish (5.0) source length and source size.

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This was taken with r.RayTracing.Shadows.AvoidSelfIntersectionTraceDistance=0.00001, though all values tried had no visible changes (other than 0 which makes it more noisy).

Example from repro project in a clean source 5.5.4 project from the UE launcher

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Steps to Reproduce

• Enable megalights with hardware RT
• Set r.RayTracing.Shadows.AvoidSelfIntersectionTraceDistance to any value greater than 0 (ex: 0.00001)
• Create a shadow casting spotlight with a Source Length > 0
• Aim it at a shadow casting mesh
• Position the camera such that the specular highlight would be in the shadow
• Note that (very noisy) light is still visible in the shadowed area