Consider this in spec:

# https://fedoraproject.org/wiki/Changes/EncourageI686LeafRemoval
%if 0%{?fedora} >= 42 || 0%{?rhel} >= 11
ExcludeArch:    %{ix86}
%endif

Zuul's mechanism will run discover-arches.py on stable Fedora (let's say, 40 or 41), and it will discover that i686 is supposed to be built.

It will then happily submit an i686 scratchbuild for rawhide (let's say, Fedora 42 or 43).

See for example https://src.fedoraproject.org/rpms/printrun/pull-request/9

Either discover-arches.py needs to run on the target system, or it needs to (un)set proper %fedora, %rhel, %epel values.