GeezerVison

@JulienPalard: Status check is done, and it's a success ✅ .

This should be backported so that the documentation built and archived for subsequent 3.8.x releases has the new generic "Docs by version" index sidebar, rather than the old out-of-date version specific one. (The current 3.8 on-line docs are already being fixed up by the docsbuild process however security branch docs are only rebuilt manually.)

@JulienPalard: Status check is done, and it's a success ✅ .

@ambv: Would you mind to merge this change into the 3.8 branch? See @ned-deily's comment.