message: Fix max iters to use unsigned.
diff: @@ -77,7 +77,7 @@ protected:
  .with_criterion(
  gko::stop::Combined::Factory::create()
  .with_criteria(gko::stop::Iteration::Factory::create()
  - .with_max_iters(246)
  + .with_max_iters(246u)
  .on_executor(gpu),
  gko::stop::ResidualNormReduction<>::
  Factory::create()
  @@ -90,7 +90,7 @@ protected:
  .with_criterion(
  gko::stop::Combined::Factory::create()
  .with_criteria(gko::stop::Iteration::Factory::create()
  - .with_max_iters(246)
  + .with_max_iters(246u)
  .on_executor(ref),
  gko::stop::ResidualNormReduction<>::
  Factory::create()
  