Update dependency webmock to v3.21.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
webmock (changelog)	'3.20.0' -> '3.21.0'

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Release Notes

bblimke/webmock (webmock)

### [`v3.21.0`](https://togithub.com/bblimke/webmock/blob/HEAD/CHANGELOG.md#3210) [Compare Source](https://togithub.com/bblimke/webmock/compare/v3.20.0...v3.21.0) - Don't use deprecated Rack::VERSION for Rack >= 3 Thanks to [Étienne Barrié](https://togithub.com/etiennebarrie) - Updated HTTPClient adapter, to build request signature using the URI after filters have been applied. Thanks to [Matt Brown](https://togithub.com/mattbnz)

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[yegor256]

@rultor please, try to merge, since 3 checks have passed

[rultor]

@rultor please, try to merge, since 3 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 3 checks have passed

@yegor256 Done! FYI, the full log is here (took me 1min)