chore(deps): update actions/checkout action to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v4.3.1 → v6.0.3

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Release Notes

actions/checkout (actions/checkout)

v6.0.3

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• Fix checkout init for SHA-256 repositories by @​yaananth in #​2439
• fix: expand merge commit SHA regex and add SHA-256 test cases by @​yaananth in #​2414

v6.0.2

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• Fix tag handling: preserve annotations and explicit fetch-tags by @​ericsciple in #​2356

v6.0.1

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v6.0.0

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v6

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v5.0.1

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What's Changed

• Port v6 cleanup to v5 by @​ericsciple in #​2301

Full Changelog: actions/checkout@v5...v5.0.1

v5.0.0

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What's Changed

• Update actions checkout to use node 24 by @​salmanmkc in #​2226
• Prepare v5.0.0 release by @​salmanmkc in #​2238

⚠️ Minimum Compatible Runner Version

v2.327.1
Release Notes

Make sure your runner is updated to this version or newer to use this release.

Full Changelog: actions/checkout@v4...v5.0.0

v5

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Note

Low Risk
Dependency-only change to the standard checkout step; no application or release logic is modified, though a major checkout bump could affect edge cases (tags, SHA-256 repos) if runners are current.

Overview
Bumps actions/checkout from v4.3.1 to v6.0.3 (pinned commit df4cb1c…) everywhere CI and release workflows check out the repo.

That covers the reusable build-gem workflow plus CI (docs and Windows jobs), manual publish, manual publish docs, and release-please publish steps. No workflow logic or inputs change—only the checkout action version.

^{Reviewed by Cursor Bugbot for commit f8192d4. Bugbot is set up for automated code reviews on this repo. Configure here.}