www/grafana: Update 12.4.0 => 12.4.2 (Fixes critical vulnerability)

Changelogs:
https://grafana.com/blog/grafana-security-release-critical-and-high-severity-security-fixes-for-cve-2026-27876-and-cve-2026-27880/
https://github.com/grafana/grafana/releases/tag/v12.4.1
https://github.com/grafana/grafana/releases/tag/v12.4.2

PR: 294105
Security: CVE-2026-27876
Security: CVE-2026-27877
Security: CVE-2026-28375
Security: CVE-2026-27879
Security: CVE-2026-27880
Security: CVE-2026-27876
Security: CVE-2026-33375
Sponsored by: UNIS Labs
MFH: 2026Q1

(cherry picked from commit bce768403c9d82c98999bbeb7aef046f14d8c952)