$ git clone -n https://src.fedoraproject.org/rpms/generic-release.git /var/lib/mock/f38-build-side-42-init-devel-777478-27875/root/chroot_tmpdir/scmroot/generic-release
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-777478-27875/root/chroot_tmpdir/scmroot/generic-release'...
$ git fetch origin df1f9efc1c5e78f060767fea016107940e0d4b70:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/generic-release
 * [new ref]         df1f9efc1c5e78f060767fea016107940e0d4b70 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at df1f9ef bump to 38 for rawhide ... actually, be clever about it and use %%fedora