TUN-8052: Update go to 1.21.5

Also update golang.org/x/net and google.golang.org/grpc to fix vulnerabilities,
although cloudflared is using them in a way that is not exposed to those risks

vendor/google.golang.org/appengine/internal/identity_flex.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by the Apache 2.0
 // license that can be found in the LICENSE file.
 
+//go:build appenginevm
 // +build appenginevm
 
 package internal