[3.11] gh-95273: Improve sqlite3.complete_statement docs (GH-95840) (#95917)

Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>
Co-authored-by: CAM Gerlach <CAM.Gerlach@Gerlach.CAM>.
(cherry picked from commit e6623e7083ce08a247e5df169bcc749f99327823)

Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>