Bad default number of BLAS threads on 1.9?

Something looks strange with the number of BLAS threads on 1.9, I think.

```julia
julia> VERSION
v"1.9.0-beta2"

julia> LinearAlgebra.BLAS.get_num_threads()
1
```

```julia
julia> VERSION
v"1.8.4"

julia> LinearAlgebra.BLAS.get_num_threads()
8
```

This should just be with everything default.

cc @staticfloat 