Proposed commit log message:
```
sysutils/py-crontab: Update to 2.4.0
- Switch from CHEESESHOP to GitLab for complete tests data
- Update the project website URL in pkg-descr
- Add LICENSE_FILE
- Add sysutils/py-cron-descriptor to RUN_DEPENDS
- Add test target
Reviewed_by: koobs, skreuzer
Approved by: koobs (ports, mentor), skreuzer (maintainer)
Differential_Revision: D23968
```