What would you like to be added?

Bump golang to

• 1.21.4 for main branch.
• 1.20.11 for 3.4 and 3.5

Reference:

• https://github.com/golang/go/issues?q=milestone%3AGo1.20.11+label%3ACherryPickApproved
• https://github.com/golang/go/issues?q=milestone%3AGo1.21.4+label%3ACherryPickApproved
• https://github.com/etcd-io/etcd/actions/runs/6808133221/job/18512089466?pr=16896

Why is this needed?

There is security fix