The code conflict doesn't block the ready status

When a PR has become ready and then another PR, of which code conflicts with the former one, was integrated, the former PR remains ready. But actually, it should have a `merge-conflict` label and should not be ready.

The PR-1469 [1] (SKARA-1588) has became ready and then PR-1472 [2] (SKARA-1817) was integrated. The PR-1469 is still ready. But actually, The PR-1469 should have a `merge-conflict` label and should not be ready (the `ready` label should be removed and the related comment aboud conflict should be added).

A normal example is PR-1409 [3]: when the code conflict occurs, the `merge-conflict` label and a related comment [4] are added.

[1] https://github.com/openjdk/skara/pull/1469
[2] https://github.com/openjdk/skara/pull/1472
[3] https://github.com/openjdk/skara/pull/1409
[4] https://github.com/openjdk/skara/pull/1409#issuecomment-1424970895