Update async-openai requirement from 0.27.1 to 0.28.0

Updates the requirements on [async-openai](https://github.com/64bit/async-openai) to permit the latest version.
- [Release notes](https://github.com/64bit/async-openai/releases)
- [Commits](64bit/async-openai@async-openai-v0.27.1...async-openai-v0.28.0)

---
updated-dependencies:
- dependency-name: async-openai
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

atlas/Cargo.toml

@@ -8,4 +8,4 @@ tokio = { workspace = true, features = ["macros"] }
 reqwest = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
-async-openai = "0.27.1"
+async-openai = "0.28.0"