Doc images are broken

I noticed "Figure 69.1. Page Layout" from the docs doesn't work on
either of the two major browsers I tested:

https://www.postgresql.org/docs/13/storage-page-layout.html

A recent regression seems likely. Is there some way that this can be
tested automatically, to avoid or at least quickly catch any would-be
regressions in the future?

Thanks
-- 
Peter Geoghegan