$ git clone -n https://src.fedoraproject.org/rpms/rust.git /var/lib/mock/f42-build-side-1-3507354-46007/root/chroot_tmpdir/scmroot/rust
Cloning into '/var/lib/mock/f42-build-side-1-3507354-46007/root/chroot_tmpdir/scmroot/rust'...
$ git fetch origin 3436f8c99bd742015560fadea6d2b0e02e631145:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust
 * [new ref]         3436f8c99bd742015560fadea6d2b0e02e631145 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3436f8c Update to Rust 1.86.0