[3.13] gh-129958: Properly disallow newlines in format specs in single-quoted f-strings (GH-130063) (GH-132692)

(cherry picked from commit 2f8b08da475152adea59b6bf98e2d0cb73dd8a59)

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>