[release/6.0] [wasm][debugger] Fix debugging an app that has another .NET Wasm instance in a service worker (#76075)

* backport 76072

* Update MonoProxy.cs

Author: thaystg

src/mono/wasm/debugger/BrowserDebugProxy/MonoProxy.cs

@@ -55,6 +55,9 @@ protected override async Task<bool> AcceptEvent(SessionId sessionId, string meth
             {
                 case "Runtime.consoleAPICalled":
                     {
+                        // Don't process events from sessions we aren't tracking
+                        if (!contexts.TryGetValue(sessionId, out ExecutionContext context))
+                            return false;
                         string type = args["type"]?.ToString();
                         if (type == "debug")
                         {
@@ -68,7 +71,6 @@ protected override async Task<bool> AcceptEvent(SessionId sessionId, string meth
                                     {
                                         // The optional 3rd argument is the stringified assembly
                                         // list so that we don't have to make more round trips
-                                        ExecutionContext context = GetContext(sessionId);
                                         string loaded = a?[2]?["value"]?.ToString();
                                         if (loaded != null)
                                             context.LoadedFiles = JToken.Parse(loaded).ToObject<string[]>();