Disable invalid `vec::as` test cases #2256

Job	Run time
check-secrets	1s
check-clang-format	7s
build-common-base-image	0s
build-image-for-sycl-impl	0s
compile-cts (computecpp, 2.11.0)	33m 52s
compile-cts (dpcpp, 8d87832f2eccc0c8dae11e1ae8009a3816f2018a)	5h 8m 37s
compile-cts (hipsycl, 3d8b1cd)	58s
cts-compiles-for-all-implementations	1s
	5h 43m 36s

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