message: Make an assert message consistent with other asserts.
diff: @@ -206,7 +206,7 @@ pub fn eval_main<'tcx>(tcx: TyCtxt<'tcx>, main_id: DefId, config: MiriConfig) ->
  let res: InterpResult<'_, i64> = (|| {
  // Main loop.
  while ecx.schedule()? {
  - assert!(ecx.step()?, "Bug: a terminated thread was scheduled for execution.");
  + assert!(ecx.step()?, "a terminated thread was scheduled for execution");
  ecx.process_diagnostics();
  }
  // Read the return code pointer *before* we run TLS destructors, to assert
  