Fix Copilot SDK session event handler compile issue (#2056)

Author: jongalloway

cookbook/copilot-sdk/dotnet/recipe/pr-visualization.cs

@@ -153,7 +153,7 @@ string PromptForRepo()
 });
 
 // Set up event handling
-session.On(evt =>
+session.On<SessionEvent>(evt =>
 {
     switch (evt)
     {