Downgrade CI fails: DifferentiationInterface incompatible with downgraded ADTypes

## Summary The Downgrade CI workflow (`alldeps` mode on Julia 1.10) fails because `DifferentiationInterface` 0.6-0.7 requires a newer version of `ADTypes` than the minimum `1.0.0` that `julia-downgrade-compat` pins. ## Details The `[compat]` section specifies: - `ADTypes = "1"` → downgraded to `1.0.0` - `DifferentiationInterface = "0.6, 0.7"` → requires ADTypes ~1.6+ When `julia-downgrade-compat` pins `ADTypes` to `1.0.0`, the resolver cannot find a compatible version of `DifferentiationInterface` within the 0.6-0.7 range: ``` DifferentiationInterface restricted to versions 0.6-0.7 by project restricted by compatibility requirements with ADTypes to versions: 0.3.0-0.3.4 or uninstalled — no versions left ADTypes restricted to versions 1 by project, leaving only versions: 1.0.0-1.21.0 restricted to versions 1.0.0 by an explicit requirement ``` Adding `DifferentiationInterface` to the `skip` list doesn't help because the `alldeps` mode still tries to resolve DI as a test dependency. ## Current Workaround The Downgrade workflow has been temporarily disabled with `if: false`. This can be re-enabled once: 1. `DifferentiationInterface` releases a version compatible with `ADTypes` 1.0.0, OR 2. The minimum `ADTypes` compat is bumped to a version that DI 0.6+ supports, OR 3. `julia-downgrade-compat` supports fully excluding packages from resolution in `alldeps` mode ## Related This is an ecosystem-level compat issue between ADTypes and DifferentiationInterface, not a bug in SciMLBase itself.