Test CGLS with shifts on rectangular systems

[amontoison]

@tmigot
I found that the size of the vectors in the workspace are not correct:
https://github.com/JuliaSmoothOptimizers/Krylov.jl/blob/main/src/krylov_solvers.jl#L1227-L1231

I will fix it in #947.
Did you never tested your solver on least-squares problems?

[amontoison]

Update: The name of the variables in the workspace were just wrong.
I fixed it in #947 and also removed the allocation by default of the additional vector needed for a preconditioner.