Make type parameter of passed in sensealg in setvjp a parameteric type from Nothing

[Vaibhavdixit02]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.79%. Comparing base (10b49a4) to head (7d77d89).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1034   +/-   ##
=======================================
  Coverage   57.79%   57.79%           
=======================================
  Files          19       19           
  Lines        4525     4525           
=======================================
  Hits         2615     2615           
  Misses       1910     1910           

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[ChrisRackauckas]

This doesn't make sense, this is a dispatch for how to set the case where vjp isn't set?

[Vaibhavdixit02]

This shows up as

ERROR: MethodError: no method matching setvjp(::GaussAdjoint{0, true, Val{:central}, ReverseDiffVJP{false}}, ::ReverseDiffVJP{f[91/414]
                                                                                                                                       
Closest candidates are:                                                                                                                
  setvjp(::SteadyStateAdjoint{CS, AD, FDT, VJP, LS, LK}, ::Any) where {CS, AD, FDT, VJP, LS, LK}                                       
   @ SciMLSensitivity ~/.julia/packages/SciMLSensitivity/ZCFhF/src/sensitivity_algorithms.jl:1107                                      
  setvjp(::GaussAdjoint{CS, AD, FDT, Nothing}, ::Any) where {CS, AD, FDT}                                                              
   @ SciMLSensitivity ~/.julia/packages/SciMLSensitivity/ZCFhF/src/sensitivity_algorithms.jl:583                                       
  setvjp(::QuadratureAdjoint{CS, AD, FDT, Nothing}, ::Any) where {CS, AD, FDT}                                                         
   @ SciMLSensitivity ~/.julia/packages/SciMLSensitivity/ZCFhF/src/sensitivity_algorithms.jl:489                                       
  ...                                                                                                                                  
                                                                                                                                       
Stacktrace:                                                                                                                            
  [1] _concrete_solve_adjoint(::ODEProblem{…}, ::Tsit5{…}, ::Nothing, ::Vector{…}, ::ComponentVector{…}, ::SciMLBase.ChainRulesOriginat
or; verbose::Bool, kwargs::@Kwargs{…})
    @ SciMLSensitivity ~/.julia/packages/SciMLSensitivity/ZCFhF/src/concrete_solve.jl:223
  [2] _concrete_solve_adjoint
    @ SciMLSensitivity ~/.julia/packages/SciMLSensitivity/ZCFhF/src/concrete_solve.jl:209 [inlined]
  [3] #_solve_adjoint#75
    @ DiffEqBase ~/.julia/packages/DiffEqBase/X5SZr/src/solve.jl:1537 [inlined]
  [4] _solve_adjoint
    @ DiffEqBase ~/.julia/packages/DiffEqBase/X5SZr/src/solve.jl:1510 [inlined]
  [5] #rrule#6
    @ DiffEqBaseChainRulesCoreExt ~/.julia/packages/DiffEqBase/X5SZr/ext/DiffEqBaseChainRulesCoreExt.jl:26 [inlined]
  [6] rrule
    @ DiffEqBaseChainRulesCoreExt ~/.julia/packages/DiffEqBase/X5SZr/ext/DiffEqBaseChainRulesCoreExt.jl:22 ```

[ChrisRackauckas]

MWE?

And no, that still doesn't motivate this PR at all. The nothing dispatch is a default setter. Deleting the default setter is not the solution...