fix(deps): update module github.com/coreos/butane to v0.28.0

[mergeraptor]

This PR contains the following updates:

Package	Change	Age	Confidence
github.com/coreos/butane	v0.27.0 → v0.28.0

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Release Notes

coreos/butane (github.com/coreos/butane)

v0.28.0

Compare Source

Starting with this release, Butane binaries are signed with the Fedora 44
key.

Features

• Stabilize OpenShift spec 4.22.0, targeting Ignition spec 3.6.0
• Add OpenShift spec 4.23.0-experimental, targeting Ignition spec 3.7.0-experimental
• Add systemd.quadlets section for embedding Podman Quadlet files (fcos 1.8.0-exp, fiot 1.1.0-exp, flatcar 1.2.0-exp, openshift 4.23.0-exp, r4e 1.2.0-exp)

Misc. changes

• Warn on root partition size is too small (fcos 1.3.0+)
• Warn on root partition constrained by another partition (fcos 1.3.0+)

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This PR has been generated by Mend Renovate.

[castrojo]

Code Review ✅

Change: Renovate bump github.com/coreos/butane v0.27.0 → v0.28.0. go.mod updated, go.sum has correct checksums (stale v0.27.0 entries removed by #218 which merged into this branch).

What's new in butane v0.28.0 (relevant to knuckle):

• systemd.quadlets section added for Flatcar 1.2.0-experimental — knuckle doesn't use this yet, no action needed
• Fedora 44 signing key for binaries — doesn't affect in-process CompileToIgnition() path
• No breaking changes to the flatcar variant we use

Safety check: knuckle compiles Butane in-process via ignition.CompileToIgnition(). The flatcar variant and version: 1.1.0 spec are unchanged in v0.28.0 — existing Ignition output is identical.

CI: re-running with updated head 5a53bd49 (post-tidy). Queuing once CI goes green.