[3.12] gh-110631: Set three-space indents for reST in EditorConfig (GH-110635) (#110637)

gh-110631: Set three-space indents for reST in EditorConfig (GH-110635)

Set three-space indents in EditorConfig
(cherry picked from commit 66a9b1082049855889854bfde617059499c26dd2)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>