Update actions/checkout action to v4

[renovate[bot]]

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`](https://togithub.com/actions/checkout/blob/HEAD/CHANGELOG.md#v400) [Compare Source](https://togithub.com/actions/checkout/compare/v3...v4) - [Support fetching without the --progress option](https://togithub.com/actions/checkout/pull/1067) - [Update to node20](https://togithub.com/actions/checkout/pull/1436)

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Configuration

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

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

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

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This PR has been generated by Mend Renovate. View repository job log here.

[yegor256]

@rultor please, try to merge, since 8 checks have passed

[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

[rultor]

@rultor please, try to merge, since 8 checks have passed

@yegor256 OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor please, try to merge, since 8 checks have passed

@yegor256 Done! FYI, the full log is here (took me 2min)