Hi,
The last kernel update for openSUSE 12.3 has been released in December, so the openSUSE-12.3 branch has been closed and removed from the mirrors. In your clone, please do
git remote prune origin git branch -D openSUSE-12.3
We are still maintaining the openSUSE-13.1 and openSUSE-13.2 branches, which contain the 3.11.10 and 3.16.7 kernels, respectively.
Michal