Update build.yml

.github/workflows/build.yml

@@ -22,8 +22,6 @@ jobs:
     - uses: actions/checkout@v1
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
-      with:
-        dotnet-version: 5.0.100
     - name: Build
       run: dotnet build -c Release
     - name: Test