Update dependency webmock to v3.20.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
webmock (changelog)	'3.19.1' -> '3.20.0'

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Release Notes

bblimke/webmock (webmock)

### [`v3.20.0`](https://togithub.com/bblimke/webmock/blob/HEAD/CHANGELOG.md#3200) [Compare Source](https://togithub.com/bblimke/webmock/compare/v3.19.1...v3.20.0) - Optimised EmHttpRequestAdapter performance. Thanks to [Ricardo Trindade](https://togithub.com/RicardoTrindade) - Removed runtime dependency on base64. Thanks to [Earlopain](https://togithub.com/Earlopain) - Typhoeus::Response objects constructed from stubbed responses now have all timing attributes set to 0.0. Thanks to [James Brown](https://togithub.com/Roguelazer) - Optimised WebMock::Util::Headers by removing redundant freeze invocations. Thanks to [Kazuhiro NISHIYAMA](https://togithub.com/znz) - The default stubbed response body, which is an empty String, is unfrozen. - When building signatures of requests made by http.rb, the request body encoding is now preserved.

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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 4min)