Avoid running traffic increase hooks after the last increase step has already been completed (and analyzed)

[pereiratps]

This PR is an improvement on the PR https://github.com/fluxcd/flagger/pull/1470 which was released in version v1.33.0.

The goal is for the traffic increase webhook to only run when the next step is actually a traffic increase.

Without this change, Flagger will still be calling the traffic increase webhook even after the last increase step has already been analyzed, right before the verification promotion webhook.

The code logic can be compared with the promotion webhook call (already on the code): https://github.com/fluxcd/flagger/blob/dfc0c96824b006d3592377f528878885ed46f6f6/pkg/controller/scheduler.go#L591-L595