SPRINGFIELD — The Illinois General Assembly returns to Springfield for its fall session this week with a light agenda borne of an upcoming election season and an unwillingness to tackle prickly issues in the short fall-session timeline.Help for Chicago in dealing with an influx of migrants from the nation’s southern border apparently will wait. But Gov. J.B. Pritzker’s vetoes of legislation to allow installation of small nuclear reactors is among the issues in play.Lawmakers are scheduled to gavel in …