Use of matrices in CI is excessive

[ocaisa]

We use CI matrices for all of the different architectures, which is creating a lot of CI jobs. Do we really need to do this though? With the EESSI module it is straightforward to reload for a different architecture target. We still probably want a matrix for each EESSI version, but I think we can just have a bash loop to loop over the architectures.

[boegel]

I agree that this should be possible, and it's probably worthwhile to change this