Add a16w8 per-op test for var #5233

Job	Run time
test-vulkan / test-backend-linux (vulkan, models) / linux-job	20m 44s
test-vulkan / test-backend-linux (vulkan, operators) / linux-job	21m 15s
test-vulkan / test-backend-macos	0s
test-vulkan / package-golden-artifacts	3m 43s
	45m 42s

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