Update build.yml

.github/workflows/build.yml

@@ -20,6 +20,8 @@ jobs:
 
       - name: Setup .NET Core
         uses: actions/setup-dotnet@master
+        with:
+          dotnet_version: '5.0.100-preview.5.20279.10'
       
       - name: Build Net_40
         run: dotnet build src/Net_40/HandyControl_Net_40/HandyControl_Net_40.csproj -p:Configuration=Release