Re-enable downgrade CI tests

[ChrisRackauckas-Claude]

Summary

The downgrade CI tests are currently disabled due to dependency resolution conflicts in the SciML ecosystem.

Details

When running with minimum compatible versions, there are unsatisfiable requirements between:

• SciMLBase
• OrdinaryDiffEqVerner
• Other SciML packages

The error shows:

ERROR: Unsatisfiable requirements detected for package OrdinaryDiffEqVerner [79d7bb75]:
 OrdinaryDiffEqVerner [79d7bb75] log:
 ├─possible versions are: 1.0.0-1.9.0 or uninstalled
 ├─restricted by compatibility requirements with SciMLBase [0bca4576] to versions: 1.0.0-1.4.0 or uninstalled

Action Items

• Monitor upstream SciML packages for compatible version releases
• Re-enable downgrade tests once dependencies are compatible
• Remove if: false from .github/workflows/Downgrade.yml

Related

This is a known issue affecting multiple SciML packages. See also:

• Re-enable downgrade tests after OrdinaryDiffEq updates DelayDiffEq.jl#356