Fix Java CI with Maven / build check

Found during review of PR #4.

See https://github.com/Simplexity-Development/AdminHax/actions/runs/16737972801/job/47381469396?pr=4.

<img width="849" height="141" alt="Image" src="https://github.com/user-attachments/assets/78b4fc21-da85-4126-ae09-781bcde2bd02" />