Update actions/checkout action to v6

[balena-renovate]

This PR contains the following updates:

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

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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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• Add worktree support for persist-credentials includeIf by @​ericsciple in #​2327

v6.0.0

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• Persist creds to a separate file by @​ericsciple in #​2286
• Update README to include Node.js 24 support details and requirements by @​salmanmkc in #​2248

v6

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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

v5.0.1

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

v5.0.0

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• Update actions checkout to use node 24 by @​salmanmkc in #​2226

v5

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

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