refactor: update dotnet to the newest version on contracts workflow

.github/workflows/chapter-4-contracts-workflow.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v3
         with:
-          dotnet-version: 7.0.x
+          dotnet-version: 8.0.x
       - name: Add GitHub NuGet Source
         run: |
           dotnet nuget add source --username $OWNER --password $GITHUB_TOKEN --store-password-in-clear-text --name github "https://nuget.pkg.github.com/$OWNER/index.json"
@@ -50,7 +50,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v3
         with:
-          dotnet-version: 7.0.x
+          dotnet-version: 8.0.x
       - name: Add GitHub NuGet Source
         run: |
           dotnet nuget add source --username $OWNER --password $GITHUB_TOKEN --store-password-in-clear-text --name github "https://nuget.pkg.github.com/$OWNER/index.json"