[UR][TEST][CUDA][HIP] Clarify known-failure rationale for CUDA/HIP kernel index checks (#21562)
Add a comment explaining why InvalidKernelArgumentIndex expectations in
urKernelSetArgValue, urKernelSetArgLocal, urKernelSetArgSampler,
urKernelSetArgMemObj, and urKernelSetArgPointer
are not meaningful for CUDA/HIP.