[3.13] gh-144693: Clarify that `PyFrame_GetBack` does not raise exceptions (GH-144824) (GH-145319)

gh-144693: Clarify that `PyFrame_GetBack` does not raise exceptions (GH-144824)
(cherry picked from commit 8775f900179aa21e6e9ec318dbb5c7cfd3561b66)

Co-authored-by: Taegyun Kim <k.taegyun@gmail.com>
Co-authored-by: Sergey Miryanov <sergey.miryanov@gmail.com>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>