ci: run SII testset in RAT downstream tests

[AayushSabharwal]

Close #31

Requires https://github.com/SciML/RecursiveArrayTools.jl/pull/362

Checklist

• [ ] Appropriate tests were added
• [ ] Any code changes were done in a way that does not break public API
• [ ] All documentation related to code changes were updated
• [ ] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• [ ] Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 35.91%. Comparing base (a7c70c8) to head (75aa870). Report is 10 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #54 +/- ## ========================================== - Coverage 38.83% 35.91% -2.93% ========================================== Files 7 7 Lines 291 401 +110 ========================================== + Hits 113 144 +31 - Misses 178 257 +79 ```

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