Add serial and 64-process Channel test to CI

[loganoz]

Expanded the CI workflow to run the Channel test in serial (1 process) and with 64 processes, in addition to the existing 8-process test. This improves coverage of different parallel configurations for the Navier-Stokes Channel solver.

[loganoz]

@psole-m, this pull request just runs develop branch (so old wall model) with 1, 8 and 64 MPI processes. Let's check if the old implementation gave the same results where it run (at least with 1 and 8 proc).

[loganoz]

@oscarmarino, is this behaviour expected?

[oscarmarino]

I think it should be the same, it is strange that we have different results. In principle the wall functions here (old one) is MPI independent, so it could be something in the channel module (I tested it in a different mesh and only a few partitions...)

[loganoz]

@oscarmarino, @psole-m I created a new test case Channel-no-source. Here I set "use channel = .false.". The runs are with 1, 8 and 64 processes. I didn't update the residuals, so I don't expect it to pass. However, if the residuals do not change, the problem is with the parallelisation of the channel source.