Update dotnet sdk version in build

Try to leverage newer language versions

.github/workflows/build.yml

@@ -21,7 +21,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1.101
+        dotnet-version: 7.0.402
     - name: Install dependencies
       run: dotnet restore
     - name: Build