ZTS: Update FreeBSD version numbers

All defined variants:

• freebsd13-4r, freebsd13-5r, freebsd14-1r, freebsd14-2r (RELEASE)
• freebsd13-5s, freebsd14-2s (STABLE)
• freebsd15-0c (CURRENT)

Used for testing:

• freebsd13-4r (RELEASE)
• freebsd14-2s (STABLE)
• freebsd15-0c (CURRENT)

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes: #17260