Add presubmit check to prevent accidental go directive bump

[sbueringer]

In CAPV we only bump the go directive in go.mod files on the main branch.

While we bump the Go minor version that we build release branches with we never bump the go directive there.

This issue is about adding a presubmit check to ensure we don't accidentally bump it.

This can be implemented by adding a new verify-go-directive Makefile target (prior art: https://github.com/kubernetes/utils/pull/306/files) and then adding it to the verify target we already run in CI.

For more context, see: https://github.com/kubernetes/kubernetes/issues/123744 and https://github.com/kubernetes-sigs/cluster-api/issues/10258

[sbueringer]

/triage accepted /help wanted

[MadhavJivrajani]

/help

[k8s-ci-robot]

@MadhavJivrajani: This request has been marked as needing help from a contributor.

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[adityabhatia]

/assign

[sbueringer]

@adityabhatia Still on your radar? :)