Update serial_test requirement from 0.8.0 to 0.9.0 (#129)

Updates the requirements on [serial_test](https://github.com/palfrey/serial_test) to permit the latest version.
- [Release notes](https://github.com/palfrey/serial_test/releases)
- [Commits](palfrey/serial_test@v0.8.0...v0.9.0)

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

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Cargo.toml

@@ -44,6 +44,6 @@ rustversion = "1.0.9"
 [dev-dependencies]
 lazy_static = "1.4.0"
 regex = "1.6.0"
-serial_test = "0.8.0"
+serial_test = "0.9.0"
 tempfile = "3.3.0"