Bump edu.hm.hafner:autograding-model from 3.25.0 to 3.28.0

Bumps [edu.hm.hafner:autograding-model](https://github.com/uhafner/autograding-model) from 3.25.0 to 3.28.0.
- [Release notes](https://github.com/uhafner/autograding-model/releases)
- [Changelog](https://github.com/uhafner/autograding-model/blob/main/CHANGELOG.md)
- [Commits](uhafner/autograding-model@v3.25.0...v3.28.0)

---
updated-dependencies:
- dependency-name: edu.hm.hafner:autograding-model
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

pom.xml

@@ -30,7 +30,7 @@
     <jib-maven-plugin.version>3.4.1</jib-maven-plugin.version>
     <testcontainers.version>1.19.7</testcontainers.version>
 
-    <autograding-model.version>3.25.0</autograding-model.version>
+    <autograding-model.version>3.28.0</autograding-model.version>
   </properties>
 
   <dependencies>