dnf is included in the installer environment, now. dnf ships:
the timer is WantedBy=basic.target , so it's enabled by default. The timer runs the service ten minutes after boot, then every hour after that. The service tries to update dnf's metadata cache. In the installer environment, it fails.
Presuming we want to turn it off for the installer, I can think of a few options. anaconda could just disable the timer at some point during boot. lorax could strip the service and timer files out. Or the service could grow some kind of Condition to disable it in the installer environment - it already has:
to stop it running in live environments, there are various Conditions that could be used somehow to disable it in the installer environment, though I don't know if any of them is entirely bulletproof (could check for stage2 on the cmdline, or the presence/absence of some particular file or directory that indicates strongly we're in the installer).