net-proxy/sing-box: add 1.9.6, drop 1.9.5

[Puqns67]

Close: #5275

[github-actions[bot]]

:heavy_check_mark: pkgcheck checks passed

• pkgcheck 0.10.30
• the corresponding ::gentoo commit: https://github.com/gentoo-mirror/gentoo/commit/936939a5c3f5204c622de23bbe1affd596fdbe48