Bump futures-task in /code-samples/serving/cloudevents/cloudevents-rust (#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](https://github.com/rust-lang/futures-rs/compare/0.3.5...0.3.28)

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

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

code-samples/serving/cloudevents/cloudevents-rust/Cargo.lock

@@ -809,12 +809,9 @@ checksum = "3f2032893cb734c7a05d85ce0cc8b8c4075278e93b24b66f9de99d6eb0fa8acc"
 
 [[package]]
 name = "futures-task"
-version = "0.3.5"
+version = "0.3.28"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bdb66b5f09e22019b1ab0830f7785bcea8e7a42148683f99214f73f8ec21a626"
-dependencies = [
- "once_cell",
-]
+checksum = "76d3d132be6c0e6aa1534069c705a74a5997a356c0dc2f86a47765e5617c5b65"
 
 [[package]]
 name = "futures-util"