Cache nuget packages

Author: ErikSchierboom

.github/workflows/ci.yml

@@ -24,6 +24,10 @@ jobs:
         uses: actions/setup-dotnet@3951f0dfe7a07e2313ec93c75700083e2005cbab
         with:
           dotnet-version: 5.0.202
+          cache: true
+
+      - name: Restore packages
+        run: dotnet restore --locked-mode
 
       - name: Run tests
         run: dotnet test