[3.11] gh-88496: Fix IDLE test hang on macOS (GH-104025) (#104027)

gh-88496: Fix IDLE test hang on macOS (GH-104025)

Replace widget.update() with widget.update_idletasks in two places.
(cherry picked from commit 4b27972f5fe816d3616f97f8643d8ad922473ab5)

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