Test model diagnostics using multiple AMPL SCIP versions

[lbianchi-lbl]

Summary/Motivation:

• Testing with multiple AMPL SCIP versions helps us having (greater) confidence that the tests affected by CI failures in test_model_diagnostics.py::TestDegeneracyHunter::test_solve_candidates_milp #1353 are written in a way that is robust to known changes between different SCIP versions
• Whether we want or need to have this test harness permanently is still being discussed
• In the meantime, we can just treat this as a "one-time jig" to validate different solutions to make the tests affected by CI failures in test_model_diagnostics.py::TestDegeneracyHunter::test_solve_candidates_milp #1353 more robust
• In other words, once the tests pass on this PR, we could just keep the fix and get rid of the other changes

Legal Acknowledgement

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1. I agree my contributions are submitted under the license terms described in the LICENSE.txt file at the top level of this directory.
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[codecov]

Codecov Report

Attention: Patch coverage is 67.56757% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 21.17%. Comparing base (4dd3c2d) to head (edb038b).

Files	Patch %	Lines
idaes/core/util/testing.py	67.56%	11 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1359       +/-   ##
===========================================
- Coverage   77.60%   21.17%   -56.44%     
===========================================
  Files         391      384        -7     
  Lines       64315    63845      -470     
  Branches    14235    14196       -39     
===========================================
- Hits        49913    13519    -36394     
- Misses      11829    50002    +38173     
+ Partials     2573      324     -2249     

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[lbianchi-lbl]

This can be closed as the relevant (non-testing-infrastructure) changes have been merged in #1360.