Also install .net 8 sdk

Author: koenbeuk

.github/workflows/build.yml

@@ -29,7 +29,9 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 9.0.x
+        dotnet-version: | 
+          8.0.x
+          9.0.x
     - name: Restore dependencies
       run: dotnet restore
     - name: Build