ftp/curl: Update to 8.20.0
Changes: https://curl.se/changes.html
Security: CVE-2026-4873, CVE-2026-5545, CVE-2026-5773, CVE-2026-6253, CVE-2026-6276, CVE-2026-6429, CVE-2026-7009, CVE-2026-7168
(cherry picked from commit a7c6b2255cf43aeb71e7203fdb79d9c71734f69a)