Update netlicensing-csharp-ci.yml

Author: r-brown

.github/workflows/netlicensing-csharp-ci.yml

@@ -14,7 +14,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: '3.1.x'
+        dotnet-version: '3.1.402'
     - name: Install dependencies
       run: dotnet restore
     - name: Build