Avoid duplicate selection step enqueueing

[ydah]

Prevent SelectionsStep from enqueueing field steps from previous selection groups more than once. continue_selections was initialized outside the group loop, so each group retained and re-enqueued every step collected from earlier groups.

For example, two groups containing first and second were enqueued as [first, first, second]. This change scopes continue_selections to each group, producing [first, second].

[rmosolgo]

Interesting ... I think the CI failures are real here. IIRC this array has something do about directives which pause execution. But I see what you mean about this array accumulating things outside of scope.

Another possible fix could be here:

graphql-ruby/lib/graphql/execution/selections_step.rb

Lines 86 to 88 in 8b9f621

	continue_selections.each do |frs|
	@runner.add_step(frs)
	end

Maybe we could do a continue_selections.clear after the steps are all passed along. (That would also let us keep using the same Array instance.)