Update dependency rack to v3.1.8

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
rack (changelog)	'3.1.7' -> '3.1.8'

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Release Notes

rack/rack (rack)

### [`v3.1.8`](https://redirect.github.com/rack/rack/compare/v3.1.7...v3.1.8) [Compare Source](https://redirect.github.com/rack/rack/compare/v3.1.7...v3.1.8)

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Configuration

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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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[yegor256]

@rultor please, try to merge, since 4 checks have passed

[rultor]

@rultor please, try to merge, since 4 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 4 checks have passed

@yegor256 Done! FYI, the full log is here (took me 9min).