Add Bool assertion in callback loop

[charleskawczynski]

To (hopefully) fix:

JET-test failed at /central/scratch/esm/slurm-buildkite/climaatmos-ci/20549/climaatmos-ci/perf/jet_report_nfailures.jl:53
--
  | Expression: #= /central/scratch/esm/slurm-buildkite/climaatmos-ci/20549/climaatmos-ci/perf/jet_report_nfailures.jl:53 =# JET.@test_opt SciMLBase.step!(integrator)
  | ═════ 1 possible error found ═════
  | ┌ step!(integrator::ClimaTimeSteppers.DistributedODEIntegrator{…}) @ ClimaTimeSteppers /central/scratch/esm/slurm-buildkite/climaatmos-ci/depot/default/packages/ClimaTimeSteppers/KGEKL/src/integrators.jl:203
  | │┌ __step!(integrator::ClimaTimeSteppers.DistributedODEIntegrator{…}) @ ClimaTimeSteppers /central/scratch/esm/slurm-buildkite/climaatmos-ci/depot/default/packages/ClimaTimeSteppers/KGEKL/src/integrators.jl:250
  | ││ runtime dispatch detected: %133::Any(%134::ClimaCore.Fields.FieldVector{Float32, @NamedTuple{c::ClimaCore.Fields.Field{…}, f::ClimaCore.Fields.Field{…}}}, %135::Float32, %126::ClimaTimeSteppers.DistributedODEIntegrator{…})::Any
  | │└────────────────────