[3.12] gh-123560: Correct docs for "empty" format type for floats (GH-123561) (#124597)

gh-123560: Correct docs for "empty" format type for floats (GH-123561)
(cherry picked from commit 274d9ab619b8150a613275835234ea9ef935f21f)

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>