Bump attohttpc from 0.28.2 to 0.28.4

Bumps [attohttpc](https://github.com/sbstp/attohttpc) from 0.28.2 to 0.28.4.
- [Release notes](https://github.com/sbstp/attohttpc/releases)
- [Commits](sbstp/attohttpc@v0.28.2...v0.28.4)

---
updated-dependencies:
- dependency-name: attohttpc
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]