update to go1.21.9

go1.21.9 (released 2024-04-03) includes a security fix to the net/http
package, as well as bug fixes to the linker, and the go/types and
net/http packages. See the [Go 1.21.9 milestone](https://github.com/golang/go/issues?q=milestone%3AGo1.21.9+label%3ACherryPickApproved)
for more details.

These minor releases include 1 security fixes following the security policy:

- http2: close connections when receiving too many headers
Maintaining HPACK state requires that we parse and process all HEADERS
and CONTINUATION frames on a connection. When a request's headers exceed
MaxHeaderBytes, we don't allocate memory to store the excess headers but
we do parse them. This permits an attacker to cause an HTTP/2 endpoint
to read arbitrary amounts of header data, all associated with a request
which is going to be rejected. These headers can include Huffman-encoded
data which is significantly more expensive for the receiver to decode
than for an attacker to send.
Set a limit on the amount of excess header frames we will process before
closing a connection.
Thanks to Bartek Nowotarski (https://nowotarski.info/) for reporting this issue.
This is CVE-2023-45288 and Go issue https://go.dev/issue/65051.

View the release notes for more information:
https://go.dev/doc/devel/release#go1.21.9

- https://github.com/golang/go/issues?q=milestone%3AGo1.21.9+label%3ACherryPickApproved
- full diff: golang/go@go1.21.8...go1.21.9

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

common.mk

@@ -17,7 +17,7 @@ CHOWN:=docker run --rm -v $(CURDIR):/v -w /v alpine chown
 DEFAULT_PRODUCT_LICENSE:=Community Engine
 PACKAGER_NAME?=
 DOCKER_GITCOMMIT:=abcdefg
-GO_VERSION:=1.21.8
+GO_VERSION:=1.21.9
 PLATFORM=Docker Engine - Community
 SHELL:=/bin/bash
 VERSION?=0.0.1-dev