Forgot to update GH workflow for release to use .NET6

Author: Warren Buckley

.github/workflows/release-nuget.yml

@@ -24,7 +24,8 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 5.0.x
+        dotnet-version: '6.0.x'
+        include-prerelease: true
 
     - name: Restore dependencies
       run: dotnet restore