build(deps): update rstest requirement from 0.20.0 to 0.21.0

Updates the requirements on [rstest](https://github.com/la10736/rstest) to permit the latest version.
- [Release notes](https://github.com/la10736/rstest/releases)
- [Changelog](https://github.com/la10736/rstest/blob/master/CHANGELOG.md)
- [Commits](la10736/rstest@v0.20.0...v0.21.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.toml

@@ -36,7 +36,7 @@ serde = { version = "1", features = ["derive"] }
 tower-http = { version = "0.5.0", features = ["full"] }
 tower = { version = "0.4.13", features = ["full"] }
 axum = { version = "0.7.1", features = ["macros", "tokio"] }
-rstest = "0.20.0"
+rstest = "0.21.0"
 speculoos = "0.11.0"
 anyhow = "1.0.61"
 hyper = "1.0.1"