Docs: forward port doc build fixes from maintenance/10.1.x

Yury Matveevrequested to merge
forward-port-doc-fixes into develop

test-docs fails on develop itself, and therefore on every MR branched from it. Sphinx runs with warnings as errors and reports two:

  • intersphinx inventory 'https://ipython.org/ipython-doc/stable/objects.inv' not fetchable ... 404
  • doc/installation.md:99: WARNING: undefined label: 'tutorial' (the label is tutorial-guide)

Both were fixed by !1038 (merged), but that MR was merged into maintenance/10.1.x and never forward ported. This is the same two-line fix on develop; the revision.md entry of !1038 (merged) is left out, as it belongs to the 10.1.6 changelog.

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