Log excerpt: Warning: Permanently added '18.207.201.161' (ED25519) to the list of known hosts.
100 28013  100 28013    0     0  1233k      0 --:--:-- --:--:-- --:--:-- 1243k
INFO: Reading stdout from command: md5sum python3-lxc-5.0.0.tar.gz

Running (timeout=18000): unbuffer mock --spec /
Comment: DNF executed by Mock is trying to check whether the package build dependencies are installable.  It appears that `rpm-build` and `systemd-rpm-macros` conflict with each other on `sysusers.attr` file (both packages provide the same package but with different content).

Log excerpt:  k
 rpm-build                   x86_64 4.18.91-3.fc38              copr_base  69
Comment: Note that `rpm-build` is installed from `copr_base` directory, not from Fedora default repositories.  It means that the `rp-build` package is "overwritten" by the Copr repository, and is non-default.  The fact that the Copr author overwrites this low-level utility looks suspicious and is likely guilty for the transaction failure.