$ git clone -n https://src.fedoraproject.org/rpms/gtkmm4.0.git /var/lib/mock/f39-build-1582213-38106/root/chroot_tmpdir/scmroot/gtkmm4.0
Cloning into '/var/lib/mock/f39-build-1582213-38106/root/chroot_tmpdir/scmroot/gtkmm4.0'...
$ git fetch origin bca7752d315bd1ce2af156228db7b69b491f90f2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gtkmm4.0
 * [new ref]         bca7752d315bd1ce2af156228db7b69b491f90f2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at bca7752 Update to 4.12.0