CI check for missing installations may ignore the easystacks actually modified in the PR

[ocaisa]

Seen in https://github.com/EESSI/software-layer/pull/1196

Now that we have the relatively cheap consistency check between architectures, the only thing we really care is the ones that are actually changed in the PR.

[ocaisa]

It is perhaps interesting to run the full check (on latest ), but that only needs to be done for one Arm and one x86 arch due to the consistency check.