$ git clone -n https://src.fedoraproject.org/rpms/jaxb-api.git /var/lib/mock/f39-build-1567795-37600/root/chroot_tmpdir/scmroot/jaxb-api
Cloning into '/var/lib/mock/f39-build-1567795-37600/root/chroot_tmpdir/scmroot/jaxb-api'...
$ git fetch origin 536a5324db2af490d7adea7eda1afcbdf1cbdc20:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/jaxb-api
 * [new ref]         536a5324db2af490d7adea7eda1afcbdf1cbdc20 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 536a532 Set ExclusiveArch on any OS with java_arches