Update workhorse renovate config to constrain go binary version
From https://gitlab.com/gitlab-org/gitlab/-/merge_requests/160022#note_2013293267:
> should we [constrain the go binary version](https://docs.renovatebot.com/golang/#go-binary-version) and have it updated automatically when we support a new go version?
>
> Also, according to [this issue comment](https://github.com/renovatebot/renovate/issues/24427#issuecomment-2068937564) it should already support `go toolchain`, maybe we are running an outdated version.
cc @nolith
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