So the line break suppression flags should be propagated through it.
Otherwise ruby invariants might break, leading to a nullptr crash in
this case.
On debug builds the assertion was this one:
https://searchfox.org/mozilla-central/rev/e6cb503ac22402421186e7488d4250cc1c5fecab/layout/generic/nsRubyBaseContainerFrame.cpp#631