Fix pagination not to be hardcoded to 25
We hardcode the number of merge requests returned per page, but never go to the next page. Looking at https://docs.gitlab.com/ee/api/merge_requests.html#list-merge-requests not limit is mentioned on how many merge requests per page can be sent. Just for the length of merge requests IDs that we found.
If we found 50 merge requests we ask for 50.