$ git clone -n https://src.fedoraproject.org/rpms/rust-backtrace-ext.git /var/lib/mock/f39-build-1572791-37791/root/chroot_tmpdir/scmroot/rust-backtrace-ext
Cloning into '/var/lib/mock/f39-build-1572791-37791/root/chroot_tmpdir/scmroot/rust-backtrace-ext'...
$ git fetch origin 5877388e3b2bc20195d99bafd2f6df4f58d5b0da:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-backtrace-ext
 * [new ref]         5877388e3b2bc20195d99bafd2f6df4f58d5b0da -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5877388 Initial import (#2242767)