fix go.sum entry for sigs.k8s.io/structured-merge-diff/v4

[jsirianni]

This resolves failed builds in ci and locally:

GOOS=darwin /Library/Developer/CommandLineTools/usr/bin/make for-all CMD="go vet ./..."
../go/pkg/mod/k8s.io/[email protected]/pkg/util/managedfields/extract.go:23:2: missing go.sum entry for module providing package sigs.k8s.io/structured-merge-diff/v4/fieldpath (imported by k8s.io/apimachinery/pkg/util/managedfields); to add:
	go get k8s.io/apimachinery/pkg/util/[email protected]
../go/pkg/mod/k8s.io/[email protected]/pkg/util/managedfields/extract.go:24:2: missing go.sum entry for module providing package sigs.k8s.io/structured-merge-diff/v4/typed (imported by k8s.io/apimachinery/pkg/util/managedfields); to add:
	go get k8s.io/apimachinery/pkg/util/[email protected]
../go/pkg/mod/k8s.io/[email protected]/pkg/runtime/converter.go:34:2: missing go.sum entry for module providing package sigs.k8s.io/structured-merge-diff/v4/value (imported by k8s.io/apimachinery/pkg/runtime); to add:
	go get k8s.io/apimachinery/pkg/[email protected]