update workflow to build with .NET 6

Author: smklancher

.github/workflows/publishrelease.yml

@@ -20,7 +20,7 @@ jobs:
       - name: Setup .NET Core
         uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: 5.0.x
+          dotnet-version: 6.0.x
 
       - name: Dump env context
         env: