Upgrade Golang to 1.21.4 and 1.20.10
What does this MR do and why?
As part of Update Golang version from 1.21.x to 1.21.4 in ... (gitlab-development-kit#1996 - closed), this MR updates the Golang version in .tool-versions
to the latest 1.21.4 and 1.20.10.
Related to gitlab-development-kit#1996 (closed)