databases/postgresql15-server: Fix PLIST

> Building package for postgresql15-server-15.r1

pkg-static: Unable to access file /usr/ports/works/usr/ports/databases/postgresql15-server/work/stage/usr/local/share/postgresql/timezone/Etc/GMT-15:No such file or directory

• Error code 1

Stop.
make: stopped in /usr/ports/databases/postgresql15-server

Approved by: portmgr (blanket)