[R] Update note about `qs` serialization #13893

Job	Run time
Build CPU	13m 21s
Build CPU ARM64 + manylinux_2_28_aarch64 wheel	3m 17s
Build CUDA + manylinux_2_28_x86_64 wheel	10m 6s
Build CUDA with RMM	10m 4s
Build CUDA with RMM (dev)	10m 23s
Build GPU-enabled R package	14m 13s
Build manylinux2014_aarch64 wheel	2m 57s
Build manylinux2014_x86_64 wheel	3m 19s
Run Python tests (single-gpu)	6m 45s
Run Google Tests with GPUs (Suite gpu, Runner linux-amd64-gpu)	4m 22s
Run Python tests (multiple-gpu)	7m 36s
Run Google Tests with GPUs (Suite gpu-rmm, Runner linux-amd64-gpu)	4m 26s
Run Python tests (cpu-amd64)	17m 58s
Run Google Tests with GPUs (Suite mgpu, Runner linux-amd64-mgpu)	2m 31s
Run Python tests (cpu-arm64)	1m 27s
	1h 52m 45s

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