[3.12] gh-102832: IDLE - update stackviewer open (GH-105528) (#105534)

gh-102832: IDLE - update stackviewer open (GH-105528)

Use 'last_exc' instead of 'last_value' in 3.12/3.
(cherry picked from commit bb3454c1a75c90da3c34c060eb23403fed3fd958)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>