www/grafana7: Security update to 7.5.12

Release notes:
https://grafana.com/docs/grafana/next/release-notes/release-notes-7-5-12/

Update to 7.5.12 with moderate severity security fix (
https://grafana.com/blog/2021/12/10/grafana-8.3.2-and-7.5.12-released-with-moderate-severity-security-fix/
)

PR: 260575
Reported by: Xander
Approved by: maintainer timeout (20 days)
MFH: 2022Q1
Security: a994ff7d-5b3f-11ec-8398-6c3be5272acd

(cherry picked from commit 55a5fd7980406185b0e0ae25346276a71ad69400)