Update tests.yaml to use dotnet 8

Author: cooolbros

.github/workflows/tests.yaml

@@ -17,7 +17,7 @@ jobs:
     - name: Install .NET Core
       uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: 7.0.x
+        dotnet-version: 8.0.x
 
     - name: Run Unit Tests
       run: dotnet test src\HUDMerger.sln