nmbug-status: Use 'show-ref --heads' for loading configs
When loading configs from Git, the bare branch name (without a
refs/heads/ prefix or similar) matches all branches of that name
(including remote-tracking branches):
.nmbug $ git show-ref config
48f3bbf1d1492e5f3d2f01de6ea79a30d3840f20 refs/heads/config
48f3bbf1d1492e5f3d2f01de6ea79a30d3840f20 refs/remotes/origin/config
4b6dbd9ffd152e7476f5101eff26747f34497cee refs/remotes/wking/config
Instead of relying on the ordering of the matching references, use
--heads to ensure we only match local branches.