www/oauth2-proxy: Update to 7.13.0

• Take maintainership.

ChangeLogs: https://github.com/oauth2-proxy/oauth2-proxy/compare/v7.8.0...v7.13.0

PR: 291807
Approved by: freebsd@rheinwolf.de (maintainer)
MFH: 2025Q4
Security: CVE-2024-34156
Security: CVE-2024-45336
Security: CVE-2024-45341
Security: CVE-2025-0913
Security: CVE-2025-4673
Security: CVE-2025-22866
Security: CVE-2025-22870
Security: CVE-2025-22871
Security: CVE-2025-22872
Security: CVE-2025-27144
Security: CVE-2025-29923
Security: CVE-2025-30204
Security: CVE-2025-47907
Security: CVE-2025-47912
Security: CVE-2025-58183
Security: CVE-2025-58186
Security: CVE-2025-64484