Update actions/checkout action to v4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v3 -> v4

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Release Notes

actions/checkout (actions/checkout)

v4

Compare Source

• Check out other refs/* by commit if provided, fall back to ref by @​orhantoy in https://github.com/actions/checkout/pull/1924

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

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• If you want to rebase/retry this PR, check this box

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This PR was generated by Mend Renovate. View the repository job log.

[0crat]

@renovate/z[bot] this pull request is too small, just 8 lines changed (less than 10), there will be no formal code review, see §53 and §28; in the future, try to make sure your pull requests are not too small; @yegor256/z please review this and merge or reject

[0crat]

Job gh:jcabi/jcabi-heroku-maven-plugin#24 is not assigned, can't get performer

[0crat]

There is an unrecoverable failure on my side. Please, submit it here:

PID: 2@0f864942-c6c9-4779-8fb6-02c62d28e407, thread: PQ-C3RUBL5H9
com.zerocracy.farm.strict.StrictProject[122] java.lang.IllegalArgumentException: File "blanks/renovate[bot].xml" is not accessible in "PMO"

1.0-SNAPSHOT: CID: d9fd1320-d3a2-45a9-a561-e17147548cee, Type: "Close job"

[0crat]

@renovate/z[bot] this pull request is too small, just 8 lines changed (less than 10), there will be no formal code review, see §53 and §28; in the future, try to make sure your pull requests are not too small; @yegor256/z please review this and merge or reject