Update CI

[eschnett]

No description provided.

[giordano]

Any reason for dropping testing for Julia v1.6? I'm uncomfortable with not testing what's the minimum supported version of a package, in fact I think that in GitHub Actions we should always use the min version, to be consistent with the Project.toml. If you believe there's a strong reason for dropping support for Julia v1.90, we could do that, but pretending that a version is supported but not testing it is less good for me.

[eschnett]

No reason, except that I'm adding the more important more modern versions. I'll add it back.

[eschnett]

OpenMPI is not working well with Julia 1.6: https://github.com/JuliaParallel/MPI.jl/actions/runs/20177999182/job/57930921483?pr=926

[eschnett]

@giordano OpenMPI_jll 5.0.9 is not working with Julia 1.6. I recall the reason is that there is no libgfortran4 version. How do we solve this?

[eschnett]

Can I get a "thumbs up" for this PR? All comments/requests are addressed, and CI is green.

[eschnett]

test_io_shared is now failing on Ubuntu as well, after reliably failing on Windows and sometimes failing on macOS. We have plastered that test with MPI_File_sync and MPI_Barrier, and I can't see what else to do.

This failing tests uses MPICH. MPICH implements the shared file pointer by creating a hidden file and storing the shared file pointer there. It then uses (file?) locking to ensure exclusive access.

@giordano Is file locking (via fcntl) implemented reliably for the file system where we're running the tests?

MPICH has special code for NFS – not sure it's using this code.

[eschnett]

I tightened the cases where we skip tests. This is now only for MPICH (for Apple and Windows). It seems OpenMPI is working fine for us all the time.

[eschnett]

I think this is good now. Do you want to have another look?