Update dotnet.yml to .NET 9

Author: stidsborg

.github/workflows/dotnet.yml

@@ -26,7 +26,7 @@ jobs:
 
       - uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: '8.0.x' # SDK Version to use; x will use the latest version of the 3.1 channel
+          dotnet-version: '9.0.x' # SDK Version to use; x will use the latest version of the 3.1 channel
 
       - name: Start containers
         run: docker compose -f "docker-compose.yml" up -d --build