dl: add go1.21.12

Change-Id: I57bfbab3db6367f0486cebc0af61ace7698439c5
Reviewed-on: https://go-review.googlesource.com/c/dl/+/596157
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: David Chase <drchase@google.com>

go1.21.12/main.go

diff --git a/go1.21.12/main.go b/go1.21.12/main.go
new file mode 100644
index 0000000..ae22747
--- /dev/null
+++ b/go1.21.12/main.go
@@ -0,0 +1,24 @@
+// Copyright 2024 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.
+
+// The go1.21.12 command runs the go command from Go 1.21.12.
+//
+// To install, run:
+//
+//	$ go install golang.org/dl/go1.21.12@latest
+//	$ go1.21.12 download
+//
+// And then use the go1.21.12 command as if it were your normal go
+// command.
+//
+// See the release notes at https://go.dev/doc/devel/release#go1.21.12.
+//
+// File bugs at https://go.dev/issue/new.
+package main
+
+import "golang.org/dl/internal/version"
+
+func main() {
+	version.Run("go1.21.12")
+}