Update attohttpc requirement from 0.27 to 0.28
Updates the requirements on [attohttpc](https://github.com/sbstp/attohttpc) to permit the latest version.
- [Release notes](https://github.com/sbstp/attohttpc/releases)
- [Commits](https://github.com/sbstp/attohttpc/compare/v0.27.0...v0.28.0)
---
updated-dependencies:
- dependency-name: attohttpc
dependency-type: direct:production
...
Signed-off-by: dependabot[bot] <support@github.com>