Bump futures from 0.3.25 to 0.3.28

Bumps [futures](https://github.com/rust-lang/futures-rs) from 0.3.25 to 0.3.28.
- [Release notes](https://github.com/rust-lang/futures-rs/releases)
- [Changelog](https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md)
- [Commits](rust-lang/futures-rs@0.3.25...0.3.28)

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

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