net-mgmt/prometheus2: Update to 2.26.1
Changes: https://github.com/prometheus/prometheus/releases/tag/v2.26.1
PR: 256324
Security: CVE-2021-29622
Security: 59ab72fb-bccf-11eb-a38d-6805ca1caf5c
Approved by: lwhsu (mentor)
(cherry picked from commit eed856cce0561df8be263b48f5ad482a096e2123)