update to go1.21.8

go1.21.8 (released 2024-03-05) includes 5 security fixes

- crypto/x509: Verify panics on certificates with an unknown public key algorithm (CVE-2024-24783, https://go.dev/issue/65390)
- net/http: memory exhaustion in Request.ParseMultipartForm (CVE-2023-45290, https://go.dev/issue/65383)
- net/http, net/http/cookiejar: incorrect forwarding of sensitive headers and cookies on HTTP redirect (CVE-2023-45289, https://go.dev/issue/65065)
- html/template: errors returned from MarshalJSON methods may break template escaping (CVE-2024-24785, https://go.dev/issue/65697)
- net/mail: comments in display names are incorrectly handled (CVE-2024-24784, https://go.dev/issue/65083)

View the release notes for more information:
https://go.dev/doc/devel/release#go1.22.1

- https://github.com/golang/go/issues?q=milestone%3AGo1.21.8+label%3ACherryPickApproved
- full diff: https://github.com/golang/go/compare/go1.21.7...go1.21.8

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

hack/dockerfiles/generate-files.Dockerfile

@@ -1,6 +1,6 @@
 # syntax=docker/dockerfile:1
 
-ARG GO_VERSION=1.21.7
+ARG GO_VERSION=1.21.8
 ARG BASE_DEBIAN_DISTRO="bookworm"
 ARG PROTOC_VERSION=3.11.4