Re-enable downgrade tests after dependency updates

[ChrisRackauckas-Claude]

Summary

The downgrade tests have been temporarily disabled in the CI workflow. This issue tracks re-enabling them once the necessary dependency updates are available.

Related

Similar to the approach taken in SciML/DelayDiffEq.jl#357

Action Items

• Monitor upstream dependency updates
• Re-enable downgrade tests when dependencies are compatible
• Remove the if: false condition from .github/workflows/Downgrade.yml