Update ci_downgrade.yml

Author: simonmandlik

.github/workflows/ci_downgrade.yml

@@ -33,6 +33,6 @@ jobs:
           arch: ${{ matrix.arch }}
       - uses: julia-actions/julia-downgrade-compat@v1
         with:
-          skip: Pkg, TOML, Statistics
+          skip: Pkg, TOML, Statistics, SparseArrays
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1