Bump julia-actions/cache from 1.5.2 to 2.0.0 (#734)

Author: dependabot[bot]

.github/workflows/exercise-tests.yml

@@ -35,7 +35,7 @@ jobs:
         with:
           version: ${{ matrix.julia-version }}
 
-      - uses: julia-actions/cache@dc1a3cdeacb521b0ca93cfc66143fcadb15a5bd0
+      - uses: julia-actions/cache@d48542bb7b6239a9391789f01d21a6bdde9ad5df
 
       - name: Install test dependencies
         run: julia --color=yes --project -e "using Pkg; Pkg.instantiate()"