git.gnome.org is no more. It has ceased to be. It's an ex-git.
Please see here:
https://about.gitlab.com/2018/05/31/welcome-gnome-to-gitlab/
Note that gitlab does not support git://, only https:// (and ssh).
[Commit message from Alexander Kanavin]
(From OE-Core rev: 8382cdc0888ca645a44aacaac1155afb8dcde979)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>