Repository entry for ::gentoo should be created with sync-git-verify-commit-signature enabled

[Flowdalic]

https://wiki.gentoo.org/wiki/Portage_with_Git recommends eselect repository enable gentoo to enable git-based sync of ::gentoo. However, this leaves sync-git-verify-commit-signature disabled, because eselect-repository does not explicitly enable sync-git-verify-commit-signature for ::gentoo and portage's default is disabled.

As much as I dislike special cases, but until https://bugs.gentoo.org/901385 is fixed, eselect-repository should enable sync-git-verify-commit-signature when creating the repos.conf entry for ::gentoo.