Update module valyala/fasthttp to v1.21.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
valyala/fasthttp	require	minor	v1.20.0 -> v1.21.0

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Release Notes

valyala/fasthttp

### [`v1.21.0`](https://togithub.com/valyala/fasthttp/releases/v1.21.0) [Compare Source](https://togithub.com/valyala/fasthttp/compare/v1.20.0...v1.21.0) - [`3cd0862`](https://togithub.com/valyala/fasthttp/commit/3cd0862) Streaming fixes ([#​970](https://togithub.com/valyala/fasthttp/issues/970)) (Erik Dubbelboer) - [`1b61ca2`](https://togithub.com/valyala/fasthttp/commit/1b61ca2) Added Protocol() as a replacement of hardcoded strHTTP11 ([#​969](https://togithub.com/valyala/fasthttp/issues/969)) (Darío) - [`52a8ab6`](https://togithub.com/valyala/fasthttp/commit/52a8ab6) fix s2b go vet warning ([#​967](https://togithub.com/valyala/fasthttp/issues/967)) (ZhangYunHao)

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[coveralls]

Pull Request Test Coverage Report for Build 574338687

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 86.594%

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Totals
Change from base Build 561077933:	0.0%
Covered Lines:	239
Relevant Lines:	276

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💛 - Coveralls