Bump futures-task in /code-samples/serving/cloudevents/cloudevents-ru…

…st (#5602)

Bumps [futures-task](https://github.com/rust-lang/futures-rs) from 0.3.5 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@0.3.5...0.3.28)

---
updated-dependencies:
- dependency-name: futures-task
  dependency-type: indirect
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>