deskutils/ganttproject: update to 2.8.9

Small improvements in pkg-plist handling

From ChangeLog: https://www.ganttproject.biz/pilsen

• Bugfixes in the user interface
• Better handling of WebDAV locks
• German translation update
• New Dutch and Israel holiday calendars.

Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D17051