dns/unbound: Update 1.25.2 => 1.26.0

Release Notes:
https://community.nlnetlabs.nl/t/unbound-1-26-0-released/3434

Changelog:
https://github.com/NLnetLabs/unbound/releases/tag/release-1.26.0

PR: 297299
Reported by: Jaap Akkerhuis <jaap@NLnetLabs.nl> (maintainer)
Approved by: osa, vvd (Mentors, implicit)
MFH: 2026Q3

(cherry picked from commit c8c07fea866d0204dc22eb091cde0dd7cd72ec40)