Check if the proper linked pull-request is evaluated

[gentlementlegen]

It is just a suspicion because it didn't happen yet, but I am not sure if the proper linked pull request is evaluated in the following scenario:

• user a opens a pull request
• user b DRAFTS a pull request
• issue is closed by user a

My suspicion is that the pull-request by user b might be evaluated because it got open last. We should make sure that the closing PR is the one that is evaluated. Again, it is just a suspicion so this scenario should be tested first (writing it down not to forget).

Relates to #128