$ git clone -n https://src.fedoraproject.org/rpms/zig.git /var/lib/mock/f43-build-side-110462-59013030-6570216/root/chroot_tmpdir/scmroot/zig
Cloning into '/var/lib/mock/f43-build-side-110462-59013030-6570216/root/chroot_tmpdir/scmroot/zig'...
$ git fetch origin 0ec1977ad7b71a299596487779ff11ca00a70212:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/zig
 * [new ref]         0ec1977ad7b71a299596487779ff11ca00a70212 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0ec1977 add default build-id to macro, correctly handle undefined macro thanks alebastr for pointing this out, unsure why I hadn't run into this myself