updated to use both .NET 8 and 9

Author: teo-nikolov

.github/workflows/github-actions-tests-on-windows.yml

@@ -9,10 +9,12 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
-      - name: Setup .NET 9 SDK
+      - name: Setup .NET 8 & 9 SDK
         uses: actions/setup-dotnet@v1.7.2
         with:
-          dotnet-version: '9.0.x'
+          dotnet-version: |
+            8.0.x
+            9.0.x
       - name: Clean
         run: dotnet clean
       - name: Install dependencies