Update actions/checkout digest to b4ffde6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	digest	8ade135 -> b4ffde6

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

[yegor256]

@rultor please, try to merge, since 6 checks have passed

[rultor]

@rultor please, try to merge, since 6 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 6 checks have passed

@yegor256 Done! FYI, the full log is here (took me 5min)

[0crat]

@renovate/z[bot] this pull request is too small, just 4 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