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

Updates the requirements on [testcontainers](https://github.com/testcontainers/testcontainers-rs) to permit the latest version.
- [Release notes](https://github.com/testcontainers/testcontainers-rs/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-rs/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-rs@0.20.0...0.21.0)

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

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

Cargo.toml

@@ -158,7 +158,7 @@ openssl = "0.10.38"
 rstest = "0.21.0"
 serial_test = "3.0.0"
 tempfile = "3.3.0"
-testcontainers = "0.20"
+testcontainers = "0.21"
 tokio = { version = "1.17.0", features = ["rt", "rt-multi-thread"] }
 tracing-subscriber = { version = "0.3.9", features = ["env-filter"] }