[Regression] Docs build broken by commit 51e46c7a4007

[Rafael J. Wysocki]

Hi Kees,

On two of my systems the docs build has been broken by commit
51e46c7a4007 ("docs, parallelism: Rearrange how jobserver reservations
are made").

The symptom is that the build system complains about the "output"
directory not being there and returns with an error.

Reverting the problematic commit makes the problem go away.

Please advise. :-)

Cheers,
Rafael