Use `:SR` instead of `SR()`

[haampie]

In ArnoldiMethod.jl 0.3 you can use :SR as a symbol instead of the struct SR(). That allows you to drop the dependency here.

However, may need to bump the julia requirement to 1.6 cause that's what ArnoldiMethod.jl has now (well, Graphs.jl too)

[simonschoelly]

I don't see any issue increasing the Julia min dependency to v1.6.