www/node20: Update to 20.18.2
Changes: https://github.com/nodejs/node/releases
https://github.com/nodejs/node/blob/main/doc/changelogs/CHANGELOG_V20.md
Security: CVE-2025-22150, CVE-2025-23083, CVE-2025-23084, CVE-2025-23085
(cherry picked from commit 19abb78c967c6f981d1125305f0a1a128f7f96b0)