Explicitly develop local OrdinaryDiffEqCore in DowngradeSublibraries CI

The julia-downgrade-compat action was not properly resolving path-based sources
in [sources] sections of Project.toml files. This caused sublibraries to try
loading OrdinaryDiffEqCore from the registry instead of the local version,
which failed because the registry version doesn't have SciMLLogging.

This fix adds an explicit Pkg.develop() step to ensure the local version of
OrdinaryDiffEqCore is used for all sublibrary tests that depend on it.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: claude

.github/workflows/DowngradeSublibraries.yml

@@ -62,6 +62,12 @@ jobs:
           projects: ${{ matrix.project }}
           skip: Pkg,TOML,Statistics,LinearAlgebra,SparseArrays,InteractiveUtils,OrdinaryDiffEqCore,OrdinaryDiffEqNonlinearSolve,OrdinaryDiffEqDifferentiation
           julia_version: ${{ matrix.julia-version }}
+      - name: Develop local OrdinaryDiffEqCore
+        if: matrix.project != 'lib/OrdinaryDiffEqCore' && matrix.project != 'lib/SimpleImplicitDiscreteSolve'
+        shell: julia --color=yes --project=${{ matrix.project }} {0}
+        run: |
+          using Pkg
+          Pkg.develop(path="lib/OrdinaryDiffEqCore")
       - uses: julia-actions/julia-buildpkg@v1
         with:
           project: ${{ matrix.project }}