[3.12] gh-110631: Fix reST indentation in `Doc/library` (GH-110685) (#110736)

gh-110631: Fix reST indentation in `Doc/library` (GH-110685)

Fix wrong indentation in the Doc/library dir.
(cherry picked from commit bb7923f556537a463c403dc1097726d8a8e1a6f2)

Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>