try to fix downgrade ci

Author: SebastianM-C

.github/workflows/Downgrade.yml

@@ -23,6 +23,7 @@ jobs:
       - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.julia-version }}
+      - run: julia --project -e 'using Pkg; Pkg.Registry.add(RegistrySpec(url  = "https://github.com/HolyLab/HolyLabRegistry.git"));'
       - uses: julia-actions/julia-downgrade-compat@v2
         with:
           skip: Pkg,TOML