Update .NET version in build workflow to 9.0.x

Author: Arlodotexe

.github/workflows/build.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v2
         with:
-          dotnet-version: 8.0.x
+          dotnet-version: 9.0.x
 
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - name: Checkout Repository