add stepsize callback

Author: vchuravy

examples/p4est_2d_dgsem/elixir_advection_basic_gpu.jl

@@ -48,7 +48,7 @@ save_solution = SaveSolutionCallback(interval = 100,
 stepsize_callback = StepsizeCallback(cfl = 1.6)
 
 # Create a CallbackSet to collect all callbacks such that they can be passed to the ODE solver
-callbacks = CallbackSet(summary_callback)
+callbacks = CallbackSet(summary_callback, stepsize_callback)
 # analysis_callback, save_solution, stepsize_callback)
 
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