Modal footer bug

We need to change the secondary action in the modal footer to another event that isn't used.

The secondary event also gets triggered for the modals close icon, which can cause some unexpected results that I just ran into.

https://gitlab.com/gitlab-org/gitlab-ui/-/blob/master/src/components/base/modal/modal.vue#L82 https://gitlab.com/gitlab-org/gitlab-ui/-/blob/master/src/components/base/modal/modal.vue#L124