SPRINGFIELD — Oral arguments slated for next month at the state’s high court feature some unusual respondents — a trio of trial judges.That’s because the Illinois Supreme Court will hear three mandamus cases when it convenes for its September term.The court’s schedule was posted this week with oral arguments slotted to take place over six days and two weeks, beginning Sept. 13 and ending Sept. 22. The term marks a return to Springfield for the justices after a summer hiatus that began after …