Let count, sum, and prod take an init kwarg

[thchr]

Allows StaticArrays' count implementation to take an init kwarg, just as Base.count (since Julia v1.6).

Also bumps StaticArrays to v1.9.8, to enable releasing the fix.

EDIT: Updated to also add init to prod and sum, fixing #1119 in the process.

[mateuszbaran]

LGTM. The invalidation action is failing but that appears to be due to some changes in Julia 1.11. Maybe we should run that action on Julia 1.10 for now or report the issue somewhere?

[thchr]

Do you want me to change CI to do that here?

EDIT: I actually don't understand why the invalidations action runs on Julia 1.11, cf.:

StaticArrays.jl/.github/workflows/Invalidations.yml

Lines 17 to 21 in 899fb0a

	runs-on: ubuntu-latest
	steps:
	- uses: julia-actions/setup-julia@v2
	with:
	version: '1'

Shouldn't version: '1' still refer to v1.10? v1.11 hasn't been released yet, right?
My bad, it has been released for a few weeks. I guess we could change the version to lts instead?

[mateuszbaran]

Yes, I think it would be a good idea to change CI script to lts here.