Fix failing test for simulate_de

[zmorrell]

The current CI build is failing 2 tests as a result OrdinaryDiffEq.jl's update to version 6.78.0. The unit tests should be evaluated and adapted to ensure that the simulate_de function is still functioning properly as a result of their recent changes. It is possible that either more stringent default error tolerances will need to be introduced for the simulate_de function or the baseline will need to be adapted.

The update makes the output value from simulate_de differ from the benchmark value by ~1e-6, so most standard user functionality that does not require high precision should be largely un-impacted.