Bump tokio in /code-samples/community/serving/helloworld-rust (#5408)

Bumps [tokio](https://github.com/tokio-rs/tokio) from 1.20.3 to 1.20.4.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](https://github.com/tokio-rs/tokio/compare/tokio-1.20.3...tokio-1.20.4)

---
updated-dependencies:
- dependency-name: tokio
  dependency-type: direct:production
...

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

code-samples/community/serving/helloworld-rust/Cargo.lock

@@ -377,9 +377,9 @@ dependencies = [
 
 [[package]]
 name = "tokio"
-version = "1.20.3"
+version = "1.20.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "664cf6576f16c0ad68184998f3c2d4be9903ede6b291a5b5cfc97d29e0057283"
+checksum = "eb78f30e4b41e98ca4cce5acb51168a033839a7af9e42b380355808e14e98ee0"
 dependencies = [
  "autocfg",
  "bytes",

code-samples/community/serving/helloworld-rust/Cargo.toml

@@ -6,5 +6,5 @@ publish = false
 
 [dependencies]
 hyper = { version = "0.14.7", features = ["full"]}
-tokio = { version = "1.20.3", features = ["macros", "rt-multi-thread"] }
+tokio = { version = "1.20.4", features = ["macros", "rt-multi-thread"] }
 pretty_env_logger = "0.4.0"