[1.7.x] Corrected indentation in docs to prevent inadvertent blockquote.
[1.7.x] Removed need to update Python version support note on each new release.

Backport of 0c06f06131c613dc4173c83ea17c68c31835fc71 from master
[1.7.x] Fixed #24015 -- Factorized create_index_sql expression

Backport of 6072f17d0 from master, with one test reinforced.
Thanks Tim Graham for the review.