$ git clone -n https://src.fedoraproject.org/rpms/rubygem-railties.git /var/lib/mock/f41-build-740691-13309/root/chroot_tmpdir/scmroot/rubygem-railties
Cloning into '/var/lib/mock/f41-build-740691-13309/root/chroot_tmpdir/scmroot/rubygem-railties'...
$ git fetch origin b0803e996eee177c7b1a20255f755aa28522ea01:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-railties
 * [new ref]         b0803e996eee177c7b1a20255f755aa28522ea01 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b0803e9 Fix FTBFS due to Minitest 5.21.0+ incompatibility.