Fix _solve with nonisbits type

[hyrodium]

This PR fixes #1069.

Before this PR

julia> using StaticArrays

julia> M = @SMatrix rand(BigFloat,3,3)
3×3 SMatrix{3, 3, BigFloat, 9} with indices SOneTo(3)×SOneTo(3):
 0.885899  0.31444   0.303044
 0.389052  0.150019  0.169436
 0.6045    0.835933  0.661603

julia> M/M
ERROR: setindex!() with non-isbitstype eltype is not supported by StaticArrays. Consider using SizedArray.
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:33
  [2] setindex!
    @ ~/.julia/dev/StaticArrays/src/MArray.jl:39 [inlined]
  [3] macro expansion
    @ ~/.julia/dev/StaticArrays/src/indexing.jl:66 [inlined]
  [4] _setindex!_scalar
    @ ~/.julia/dev/StaticArrays/src/indexing.jl:46 [inlined]
  [5] setindex!
    @ ~/.julia/dev/StaticArrays/src/indexing.jl:42 [inlined]
  [6] macro expansion
    @ ~/.julia/dev/StaticArrays/src/indexing.jl:357 [inlined]
  [7] _setindex!
    @ ~/.julia/dev/StaticArrays/src/indexing.jl:320 [inlined]
  [8] setindex!
    @ ~/.julia/dev/StaticArrays/src/indexing.jl:274 [inlined]
  [9] _solve
    @ ~/.julia/dev/StaticArrays/src/solve.jl:36 [inlined]
 [10] \
    @ ~/.julia/dev/StaticArrays/src/solve.jl:1 [inlined]
 [11] /(A::SMatrix{3, 3, BigFloat, 9}, B::SMatrix{3, 3, BigFloat, 9})
    @ LinearAlgebra ~/julia/julia-1.7.3/share/julia/stdlib/v1.7/LinearAlgebra/src/generic.jl:1152
 [12] top-level scope
    @ REPL[3]:1

After this PR

julia> using StaticArrays

julia> M = @SMatrix rand(BigFloat,3,3)
3×3 SMatrix{3, 3, BigFloat, 9} with indices SOneTo(3)×SOneTo(3):
 0.942716  0.114509  0.0781129
 0.904454  0.745812  0.0366264
 0.101574  0.791193  0.193288

julia> M/M
3×3 SMatrix{3, 3, BigFloat, 9} with indices SOneTo(3)×SOneTo(3):
 1.0  -4.34983e-78  4.93776e-78
 0.0   1.0          0.0
 0.0   0.0          1.0

[hyrodium]

x-ref :#749
If the PR is resolved, we might not need this PR #1071.

[hyrodium]

I think we can merge this PR since merging #749 might take time and this PR just fixes the issue.