Re-enable downgrade tests after dependency compatibility is resolved

[ChrisRackauckas-Claude]

Summary

The downgrade CI tests have been temporarily disabled in #369 due to dependency compatibility issues with the minimum version bounds after bumping Turing.jl to 0.42.

Details

The downgrade tests fail because the minimum version bounds in [compat] are incompatible with the latest Turing.jl 0.42.x. This is a known issue that affects multiple packages in the ecosystem.

Action Items

• Monitor upstream dependency updates
• Update minimum version bounds as needed for compatibility
• Re-enable downgrade tests by removing if: false from .github/workflows/Downgrade.yml

Related

• PR Use SciMLBase.AbstractSciMLProblem and bump Turing.jl to 0.42 #369: Use SciMLBase.AbstractSciMLProblem and bump Turing.jl to 0.42