URLs with trailing / make the tests fail

[Yannick-Dayer]

Turns out the fix in #4 was not enough, as the actual URLs passed to sphinx come from Catalog and most URLs will contain a / at then end.

Apparently sphinx >= 8.0 appends /objects.inv at the end of the URL, resulting in double /.
The error is corrected by sphinx later on so it still works:

loading intersphinx inventory 'numpy' from https://numpy.org/doc/stable//objects.inv ...
intersphinx inventory has moved: https://www.sphinx-doc.org/en/master//objects.inv -> https://www.sphinx-doc.org/en/master/objects.inv

But our tests only look at the loading intersphinx inventory line so they fail.

Either we ask sphinx to revert to the same behavior as before, we add a check to remove the trailing / at the end of every URL in Catalog, or we change the tests to allow the //.