Skeletal Mesh BLAS updates when not animating

The BLAS for Skeletal Meshes that don't move, or tick get updated every frame even if the animation and skin cache aren't updated. This adds over 1ms to update time.

The only exception is if the skeletal mesh is set to `bRenderStatic`, which puts the mesh in ref pose. But we want to have it retain the pose that was set. Exporting the posed mesh as a static mesh isn't an option either since we want them to ragdoll and respond to player interaction.

Steps to Reproduce

1. Place a skeletal mesh in a level or open the attached project which has a skeletal mesh in a level and ray tracing enabled
2. enter PIE
3. run the console command `STAT D3D12RayTracing`

Expected
No BLAS update occurs for skeletal mesh that isn't animating

Actual
BLAS update occurs because the GPUSkin cache is causing FSkeletalMeshObjectGPUSkin::UpdateRayTracingGeometry_Internal to be called.