FIX: Sphinx extlinks definition

Just updating the extlinks definition in the docs configuration to avoid CI errors

@mercadil @teichman

LGTM

This is successfully built on XFEL RTD as well: https://rtd.xfel.eu/docs/scs-toolbox/en/fix-ci-autoapi-failure/changelog.html

I'll merge it now, thanks for the review!

merged

mentioned in commit a7db1a8d

mentioned in commit 489c7c21