Update Go 1.20 and 1.21

What does this MR do and why?

Update Go versions

https://go.dev/doc/devel/release#go1.21.0:

go1.21.5 (released 2023-12-05) includes security fixes to the go command, and the net/http and path/filepath packages, as well as bug fixes to the compiler, the go command, the runtime, and the crypto/rand, net, os, and syscall packages. See the Go 1.21.5 milestone on our issue tracker for details.

go1.20.12 (released 2023-12-05) includes security fixes to the go command, and the net/http and path/filepath packages, as well as bug fixes to the compiler and the go command. See the Go 1.20.12 milestone on our issue tracker for details.

Go Milestones:

• 1.20.12: https://github.com/golang/go/issues?q=milestone%3AGo1.20.12+label%3ACherryPickApproved
• 1.21.5: https://github.com/golang/go/issues?q=milestone%3AGo1.21.5+label%3ACherryPickApproved

Realated MRs:

• Omnibus Builder: gitlab-omnibus-builder!323 (merged)
• Omnibus: TBD
• CNG: TBD

Closes #133 (closed)

Checklist

• (If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.