[flakiness] Fix timeout flakiness in //test/core/end2end:cancel_after_invoke_test

Based on discussions with drfloob@

PiperOrigin-RevId: 596958525

src/core/ext/transport/chttp2/server/chttp2_server.cc

@@ -617,8 +617,17 @@ void Chttp2ServerListener::ActiveConnection::Start(
   RefCountedPtr<HandshakingState> handshaking_state_ref;
   listener_ = std::move(listener);
   {
-    MutexLock lock(&mu_);
-    if (shutdown_) return;
+    ReleasableMutexLock lock(&mu_);
+    if (shutdown_) {
+      lock.Release();
+      // If the Connection is already shutdown at this point, it implies the
+      // owning Chttp2ServerListener and all associated ActiveConnections have
+      // been orphaned. The generated endpoints need to be shutdown here to
+      // ensure the tcp connections are closed appropriately.
+      grpc_endpoint_shutdown(endpoint, absl::OkStatus());
+      grpc_endpoint_destroy(endpoint);
+      return;
+    }
     // Hold a ref to HandshakingState to allow starting the handshake outside
     // the critical region.
     handshaking_state_ref = handshaking_state_->Ref();