Remove unsupported Julia versions from Buildkite tests.
Created by: maleadt
CUDA.jl, Metal.jl, oneAPI.jl and AMDGPU.jl are all being develop
ed here, however, the current master branches of said packages only support Julia 1.10+, leading to all these tests failing all the time. Remove the older Julia versions from the roster, except for the Enzyme job where CUDA is add
ed.