add wb_back on all task switch paths (#60617)
Since this task's stack or scope field could have been modified after it
was marked by an incremental collection (and not just for copy stacks),
move the barrier back unconditionally here.
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Co-authored-by: Valentin Churavy <v.churavy@gmail.com>
Co-authored-by: Jeff Bezanson <jeff.bezanson@gmail.com>
