Fix failing testStatus

This PR should fix the status checking logic to be used in the merge commands. The paginated list of statuses returned by `get_statuses()` used to be reversed to pick the last status. This caused the `TestMerge.testStatus` to fail since the "pending" status was always picked up. This PR:

- remove the `reversed` operation in `get_statuses()`
- add extra asserts in the `testStatus` test method to check the state of the first status of the paginated list is equal to the state set by the `commit.create_status` call

Testing: this PR should turn the integration tests run by `SCC-self-merge` green again.