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/golang.org/x/sync/errgroup/pre_go120.go

@@ -0,0 +1,15 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.20
+// +build !go1.20
+
+package errgroup
+
+import "context"
+
+func withCancelCause(parent context.Context) (context.Context, func(error)) {
+	ctx, cancel := context.WithCancel(parent)
+	return ctx, func(error) { cancel() }
+}