Fix get() ambiguities

Done by:

1. Constraining the type parameter to AbstractVector{Symbol}
2. Modifying the method below it to use a vector instead of a tuple

src/optimisation/Optimisation.jl

@@ -277,13 +277,13 @@ StatsBase.loglikelihood(m::ModeResult) = m.lp
 
 """
  Base.get(m::ModeResult, var_symbol::Symbol)
- Base.get(m::ModeResult, var_symbols)
+ Base.get(m::ModeResult, var_symbols::AbstractVector{Symbol})
 
 Return the values of all the variables with the symbol(s) `var_symbol` in the mode result
 `m`. The return value is a `NamedTuple` with `var_symbols` as the key(s). The second
-argument should be either a `Symbol` or an iterator of `Symbol`s.
+argument should be either a `Symbol` or a vector of `Symbol`s.
 """
-function Base.get(m::ModeResult, var_symbols)
+function Base.get(m::ModeResult, var_symbols::AbstractVector{Symbol})
  log_density = m.f
  # Get all the variable names in the model. This is the same as the list of keys in
  # m.values, but they are more convenient to filter when they are VarNames rather than
@@ -304,7 +304,7 @@ function Base.get(m::ModeResult, var_symbols)
  return (; zip(var_symbols, value_vectors)...)
 end
 
-Base.get(m::ModeResult, var_symbol::Symbol) = get(m, (var_symbol,))
+Base.get(m::ModeResult, var_symbol::Symbol) = get(m, [var_symbol])
 
 """
  ModeResult(log_density::OptimLogDensity, solution::SciMLBase.OptimizationSolution)