Update `unstable` images to Go 1.22rc1

[Adam Chalkley]

From the release announcement (https://groups.google.com/g/golang-announce/c/FIUY9kd7fc0) on 2023-12-19:

Hello gophers,

We have just released go1.22rc1, a release candidate version of Go 1.22.
It is cut from release-branch.go1.22 at the revision tagged go1.22rc1.

Please try your production load tests and unit tests with the new version.
Your help testing these pre-release versions is invaluable.

Report any problems using the issue tracker:
https://go.dev/issue/new

If you have Go installed already, an easy way to try go1.22rc1
is by using the go command:
$ go install golang.org/dl/go1.22rc1@latest
$ go1.22rc1 download

You can download binary and source distributions from the usual place:
https://go.dev/dl/#go1.22rc1

To find out what has changed in Go 1.22, read the draft release notes:
https://tip.golang.org/doc/go1.22

Cheers,
Than and Carlos for the Go team