$ git clone -n https://src.fedoraproject.org/rpms/swift-lang.git /var/lib/mock/f39-build-2546883-61806/root/chroot_tmpdir/scmroot/swift-lang
Cloning into '/var/lib/mock/f39-build-2546883-61806/root/chroot_tmpdir/scmroot/swift-lang'...
$ git fetch origin b1cf890222c620e4be45ae54a48fb6c1ac52465a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/swift-lang
 * [new ref]         b1cf890222c620e4be45ae54a48fb6c1ac52465a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b1cf890 Updated to Swift-5.9-RELEASE