I really don't like to flag the distcheck job as allowed to fail, but
the issue we have with it right now (#5790) is very annoying and I have
no idea where the weird uncleaned files come from. I can't reproduce
this locally and these files are seemingly never created here during a
distcheck.
Since it makes all our pipelines fail, this makes it harder to diagnose
and find real other bugs, so let's allow failure until we figure this
out.