docs.s.o build broken, lots of 404, no TOC

Tonight's docs.s.o build "worked", but the doc is broken. At https://docs.softwareheritage.org/devel/ I notice at least:

• no TOC
• lots of 404, e.g., https://docs.softwareheritage.org/devel/swh-model/persistent-identifiers.html , https://docs.softwareheritage.org/devel/swh-web-client/
• no clickable links on the list of modules

It looks like no submodule has its documentation built.

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Migrated from T2386 (view on Phabricator)