`DimensionError` when computing `inv` of a StaticArray

Computing inverse of a `StaticArray` results in a `DimensionError`:
```julia
julia> using Unitful, StaticArrays, LinearAlgebra

julia> N = (@SMatrix [2 5; 1 3])u"Å"
2×2 SMatrix{2, 2, Quantity{Int64, 𝐋, Unitful.FreeUnits{(Å,), 𝐋, nothing}}, 4} with indices SOneTo(2)×SOneTo(2):
2 Å 5 Å
1 Å 3 Å

julia> inv(N)
ERROR: DimensionError: Å and 3.0 Å^-1 are not dimensionally compatible.
Stacktrace:
[1] convert(#unused#::Type{Quantity{Float64, 𝐋, Unitful.FreeUnits{(Å,), 𝐋, nothing}}}, x::Quantity{Float64, 𝐋^-1, Unitful.FreeUnits{(Å^-1,), 𝐋^-1, nothing}})
@ Unitful ~/.julia/packages/Unitful/SUQzL/src/conversion.jl:112
[2] macro expansion
@ ~/.julia/packages/StaticArrays/58yy1/src/util.jl:17 [inlined]
[3] convert_ntuple
@ ~/.julia/packages/StaticArrays/58yy1/src/util.jl:13 [inlined]
[4] SMatrix{2, 2, Quantity{Float64, 𝐋, Unitful.FreeUnits{(Å,), 𝐋, nothing}}, 4}(x::NTuple{4, Quantity{Float64, 𝐋^-1, Unitful.FreeUnits{(Å^-1,), 𝐋^-1, nothing}}})
@ StaticArrays ~/.julia/packages/StaticArrays/58yy1/src/SArray.jl:28
[5] _inv
@ ~/.julia/packages/StaticArrays/58yy1/src/inv.jl:15 [inlined]
[6] inv(A::SMatrix{2, 2, Quantity{Int64, 𝐋, Unitful.FreeUnits{(Å,), 𝐋, nothing}}, 4})
@ StaticArrays ~/.julia/packages/StaticArrays/58yy1/src/inv.jl:5
[7] top-level scope
@ REPL[13]:1
```

This doesn't occur if I am using normal arrays:
```julia
julia> M = [2 5; 1 3]u"Å"
2×2 Matrix{Quantity{Int64, 𝐋, Unitful.FreeUnits{(Å,), 𝐋, nothing}}}:
2 Å 5 Å
1 Å 3 Å

julia> inv(M)
2×2 reinterpret(Quantity{Float64, 𝐋^-1, Unitful.FreeUnits{(Å^-1,), 𝐋^-1, nothing}}, ::Matrix{Float64}):
3.0 Å^-1 -5.0 Å^-1
-1.0 Å^-1 2.0 Å^-1
```

Reproduce the failure with the Unitful and StaticArrays example, then compare it with the normal Matrix result. Start at the StaticArrays inv.jl path and the Unitful conversion.jl path shown in the stack trace; done means inv(N) succeeds and returns the expected inverse quantities with inverse units.

Written by the indexing model from the issue text.