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 18 checks have passed

[rultor]

@rultor please, try to merge, since 18 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 18 checks have passed

@yegor256 Done! FYI, the full log is here (took me 23min).