build(deps): bump azure_identity from 0.20.0 to 0.21.0

Bumps [azure_identity](https://github.com/azure/azure-sdk-for-rust) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/azure/azure-sdk-for-rust/releases)
- [Changelog](https://github.com/Azure/azure-sdk-for-rust/blob/main/HISTORY.md)
- [Commits](https://github.com/azure/azure-sdk-for-rust/commits/azure_identity-0.21.0)

---
updated-dependencies:
- dependency-name: azure_identity
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Cargo.toml

@@ -12,7 +12,7 @@ license = "MIT"
 clap = { version = "4.5.20", features = ["derive", "cargo"] }
 tokio = { version = "^1.40.0", features = ["macros", "rt-multi-thread"] }
 azure_core = "^0.20"
-azure_identity = "^0.20"
+azure_identity = "^0.21"
 azure_svc_batch = "^0.20"
 url = "2.5.2"
 reqwest = { version = "0.12.8", features = ["json"] }