net/gotify-server: fixed error message in Makefile

The exact errors appear below.

net/gotify-server:

This command (FreshPorts code 1):

/usr/local/bin/sudo /usr/sbin/jexec freshports /make-port.sh /usr/ports
net/gotify-server
2>/tmp/FreshPorts.net.gotify-server.make-error.2024.10.26.8.33.5.9820

produced this error:

Error message is: make: "/usr/ports/net/gotify-server/Makefile" line
30: Malformed conditional (${OPSYS} == FreeBSD && ${OSVERSION} >=

make: Fatal errors encountered -- cannot continue
Make results are : make: stopped in /usr/ports/net/gotify-server

Reported by: dan@langille.org