Bump julia-actions/cache from 2 to 3 (#118)

Author: dependabot[bot]

.github/workflows/downgrade.yml

@@ -24,6 +24,6 @@ jobs:
       - uses: julia-actions/julia-downgrade-compat@v2
         with:
           skip: Pkg,TOML,InteractiveUtils,Random,LinearAlgebra
-      - uses: julia-actions/cache@v2
+      - uses: julia-actions/cache@v3
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1