Update strum requirement from 0.27 to 0.28

Updates the requirements on [strum](https://github.com/Peternator7/strum) to permit the latest version.
- [Release notes](https://github.com/Peternator7/strum/releases)
- [Changelog](https://github.com/Peternator7/strum/blob/master/CHANGELOG.md)
- [Commits](Peternator7/strum@v0.27.0...v0.28.0)

---
updated-dependencies:
- dependency-name: strum
  dependency-version: 0.28.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

cdx-core/Cargo.toml

@@ -97,7 +97,7 @@ der = { version = "0.8", features = ["std"], optional = true }
 chrono = { version = "0.4", features = ["serde", "now"], default-features = false }
 
 # Derive macros for Display/AsRefStr
-strum = { version = "0.27", features = ["derive"] }
+strum = { version = "0.28", features = ["derive"] }
 
 # Error handling
 thiserror = "2.0"