Missing zero_last_degree!

Hi! We are currently integrating SpeedyWeather into our modelling activities. However, with the new releases v0.18.0 and v0.18.1 we now encounter a runtime error, where the model crashes on the `run!` call with the following error: ``` ERROR:` UndefVarError: `zero_last_degree!` not defined in `SpeedyWeather` ``` To make sure that this was not due to our setup, we tried with the given 3D example for **Jablonowski-Williamson baroclinic wave** as: ``` using SpeedyWeather spectral_grid = SpectralGrid(trunc=31, nlayers=8, Grid=FullGaussianGrid, dealiasing=3) orography = ZonalRidge(spectral_grid) initial_conditions = InitialConditions( vordiv = ZonalWind(spectral_grid), temp = JablonowskiTemperature(spectral_grid), pres = ConstantPressure(spectral_grid)) model = PrimitiveDryModel(spectral_grid; orography, initial_conditions, physics=false) simulation = initialize!(model) run!(simulation, period=Day(9)) ``` which resulted in the following: ``` julia> run!(simulation, period=Day(20)) ERROR: UndefVarError: `zero_last_degree!` not defined in `SpeedyWeather` Suggestion: check for spelling errors or missing imports. Stacktrace: [1] implicit_correction!(diagn::DiagnosticVariables{…}, progn::PrognosticVariables{…}, implicit::ImplicitPrimitiveEquation{…}, model::PrimitiveWetModel{…}) @ SpeedyWeather ~/.julia/packages/SpeedyWeather/hKf2u/src/dynamics/implicit.jl:376 [2] timestep!(progn::PrognosticVariables{…}, diagn::DiagnosticVariables{…}, dt::Float32, model::PrimitiveWetModel{…}, lf1::Int64, lf2::Int64) @ SpeedyWeather ~/.julia/packages/SpeedyWeather/hKf2u/src/dynamics/time_integration.jl:394 [3] first_timesteps!(progn::PrognosticVariables{…}, diagn::DiagnosticVariables{…}, model::PrimitiveWetModel{…}) @ SpeedyWeather ~/.julia/packages/SpeedyWeather/hKf2u/src/dynamics/time_integration.jl:281 [4] first_timesteps! @ ~/.julia/packages/SpeedyWeather/hKf2u/src/dynamics/time_integration.jl:244 [inlined] [5] timestep!(simulation::Simulation{PrimitiveWetModel{…}, PrognosticVariables{…}, DiagnosticVariables{…}}) @ SpeedyWeather ~/.julia/packages/SpeedyWeather/hKf2u/src/dynamics/time_integration.jl:418 [6] time_stepping! @ ~/.julia/packages/SpeedyWeather/hKf2u/src/dynamics/time_integration.jl:446 [inlined] [7] run!(simulation::Simulation{PrimitiveWetModel{…}, PrognosticVariables{…}, DiagnosticVariables{…}}; period::Day, steps::Int64, output::Bool) @ SpeedyWeather ~/.julia/packages/SpeedyWeather/hKf2u/src/models/simulation.jl:43 [8] top-level scope @ REPL[8]:1 ```