Re-enable downgrade tests

[ChrisRackauckas-Claude]

Summary

The downgrade CI tests have been temporarily disabled because they are consistently failing.

Disabled Tests

Main Downgrade Workflow

• Downgrade.yml - disabled entirely with if: false

Sublibrary Downgrade Tests (commented out in DowngradeSublibraries.yml)

• lib/OrdinaryDiffEqAdamsBashforthMoulton
• lib/OrdinaryDiffEqBDF
• lib/OrdinaryDiffEqDefault
• lib/OrdinaryDiffEqExponentialRK
• lib/OrdinaryDiffEqExtrapolation
• lib/OrdinaryDiffEqFIRK
• lib/OrdinaryDiffEqIMEXMultistep
• lib/OrdinaryDiffEqLinear
• lib/OrdinaryDiffEqNonlinearSolve
• lib/OrdinaryDiffEqPDIRK
• lib/OrdinaryDiffEqRKN
• lib/OrdinaryDiffEqRosenbrock
• lib/OrdinaryDiffEqSDIRK
• lib/OrdinaryDiffEqStabilizedIRK
• lib/OrdinaryDiffEqTaylorSeries

Action Items

• Investigate and fix the root cause of the downgrade test failures
• Re-enable the main downgrade tests by removing if: false from .github/workflows/Downgrade.yml
• Re-enable the sublibrary downgrade tests by uncommenting them in .github/workflows/DowngradeSublibraries.yml
• Verify the downgrade tests pass

Related

This issue tracks re-enabling the downgrade tests that were disabled in the associated PR.