fix julia-downgrade-compat@v2 usage

Co-authored-by: Claude <[email protected]>

Author: SebastianM-C

.github/workflows/DowngradeSublibraries.yml

@@ -48,7 +48,7 @@ jobs:
         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:
-          project: ${{ matrix.project }}
+          projects: ${{ matrix.project }}
           skip: Pkg,TOML,LinearAlgebra,Logging,Printf,Random,SparseArrays,Test
       - uses: julia-actions/julia-buildpkg@v1
         with: