Update blank-csharp aws-lambda-tools-defaults.json to use net6.0 framework and dotnet6 runtime

Author: AWStimrtrev

sample-apps/blank-csharp/src/blank-csharp/aws-lambda-tools-defaults.json

@@ -11,8 +11,8 @@
   "profile":"default",
   "region" : "us-east-2",
   "configuration" : "Release",
-  "framework" : "netcoreapp3.1",
-  "function-runtime":"dotnetcore3.1",
+  "framework" : "net6.0",
+  "function-runtime":"dotnet6",
   "function-memory-size" : 512,
   "function-timeout" : 30,
   "function-handler" : "blank-csharp::blankCsharp.Function::FunctionHandler"