Update actions/checkout action to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v5 -> v6

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Release Notes

actions/checkout (actions/checkout)

v6

Compare Source

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Configuration

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[yegor256]

@rultor please, try to merge, since 14 checks have passed

[rultor]

@rultor please, try to merge, since 14 checks have passed

@renovate[bot] @yegor256 Can't merge it. Some CI checks failed. Apparently, the pull request is not ready to be merged since it has some problems. Please fix them first.