Building HTML documentation with Sphinx fails

[jesper-friis]

The CI tests has started to fail during building html documentation.

See e.g. https://github.com/SINTEF/dlite/actions/runs/6315823932/job/17178291422?pr=649 which gives the following error message:

[100%] Building HTML documentation with Sphinx

Extension error (autoapi.extension):
Handler <function run_autoapi at 0x7f424231eee0> for event 'builder-inited' threw an exception (exception: 'Module' object has no attribute 'doc')
make[2]: *** [doc/CMakeFiles/Sphinx.dir/build.make:75: doc/html/index.html] Error 2
make[1]: *** [CMakeFiles/Makefile2:3252: doc/CMakeFiles/Sphinx.dir/all] Error 2
make: *** [Makefile:166: all] Error 2
Error: Process completed with exit code 2.