build(deps): update rstest requirement from 0.20 to 0.21

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] <[email protected]>

Cargo.toml

@@ -55,7 +55,7 @@ tokio = { version = "1", default_features = false }
 cfg-if = "1.0"
 
 [dev-dependencies]
-rstest = "0.20"
+rstest = "0.21"
 tempfile = "3.2"
 textwrap = "0.16"
 testcontainers = "0.17.0"