[release-v1.21] Update buildkit to v0.28.1

[dsimansk]

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[openshift-ci]

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[openshift-ci]

@dsimansk: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/421-images	39a5168	link	true	/test 421-images
ci/prow/421-e2e-oncluster-test	39a5168	link	true	/test 421-e2e-oncluster-test

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