Bump httptools from 0.6.1 to 0.6.4

Bumps [httptools](https://github.com/MagicStack/httptools) from 0.6.1 to 0.6.4.
- [Release notes](https://github.com/MagicStack/httptools/releases)
- [Commits](MagicStack/httptools@v0.6.1...v0.6.4)

---
updated-dependencies:
- dependency-name: httptools
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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