[Security] Bump http from 0.1.15 to 0.1.21 in /rust

Bumps [http](https://github.com/hyperium/http) from 0.1.15 to 0.1.21. **This update includes security fixes.**
- [Release notes](https://github.com/hyperium/http/releases)
- [Changelog](https://github.com/hyperium/http/blob/v0.1.21/CHANGELOG.md)
- [Commits](hyperium/http@v0.1.15...v0.1.21)

Signed-off-by: dependabot-preview[bot] <[email protected]>