allow Trixi.jl v0.16

[ranocha]

It looks like there are no downgrade tests in TrixiShallowWater.jl. If so, we cannot test both the old version v0.15 and the new version v0.16 of Trixi.jl in CI. I would like to avoid supporting versions that are not tested in CI. Thus, I see two options here:

• Restrict TrixiShallowWater.jl to Trixi.jl v0.16 (although this is not required in terms of features).
• Add downgrade CI tests similar to Trixi.jl.

What do you think about this, @andrewwinters5000 and @patrickersing?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.28%. Comparing base (01ae544) to head (483ac79).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #133   +/-   ##
=======================================
  Coverage   99.28%   99.28%           
=======================================
  Files          96       96           
  Lines        5146     5146           
=======================================
  Hits         5109     5109           
  Misses         37       37           

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[andrewwinters5000]

I see in Trixi the downgrade runs the test/test_threaded.jl which includes a smattering of elixirs across the different mesh types and features. We would need to assemble some small subset of test elixirs to do the same I suppose. And then we could add a Downgrade.yml to the CI workflow.

[ranocha]

Yes, this would be ideal, I think.

[patrickersing]

We already have a collection of representative tests in test_upstream.jl. Should we just reuse the same testset for the downgrade testing?

[patrickersing]

We have added a downgrade CI test in #134

[ranocha]

Thanks! Let's see what CI tells us.

[patrickersing]

LGTM! All CI tests have passed.