Use actions/cache@v3

Hoping to get rid of this warning when running the _Retrieve cached NuGet packages_ step:
> The `save-state` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Author: 0xced

.github/workflows/continuous-integration.yml

@@ -35,10 +35,12 @@ jobs:
       - name: Install .NET SDK
         uses: actions/setup-dotnet@v1
       - name: Retrieve cached NuGet packages
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: ~/.nuget/packages
           key: ${{ runner.os }}-nuget-${{ hashFiles('**/packages.lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget-
       - name: Restore NuGet packages
         run: dotnet restore
       - name: Build solution