$ git clone -n https://src.fedoraproject.org/rpms/vdirsyncer.git /var/lib/mock/f40-build-2719793-73017/root/chroot_tmpdir/scmroot/vdirsyncer
Cloning into '/var/lib/mock/f40-build-2719793-73017/root/chroot_tmpdir/scmroot/vdirsyncer'...
$ git fetch origin b4d39fa52afe665deef152a5e283ff558e0204a9:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/vdirsyncer
 * [new ref]         b4d39fa52afe665deef152a5e283ff558e0204a9 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b4d39fa fix version from github PR: Bump constraint for aiostream #1112