Change the merge check warning for unsuccessful builds

We should hange the description to something a little less misleading, but I don't know what would be the best description here.

Now I can imagine a situation when there are 3 builds for each commit, and when you choose that, you need at least one successful build on the last commit from the dropdown it means that you need 3 to pass. It should be more like:

I need one successful build from each build system on the last commit.