In short, the logical branch names should match between the build configuration and the versioned settings root.
Your versioned settings root and the root attached to the [PR configuration](https://teamcity.jetbrains.com/admin/editBuildTypeVcsRoots.html?init=1&id=buildType:Checkstyle_IdeaInspectionsPullRequest&_gl=1*mduotk*_ga*MTYzMTM1MzI2MS4xNjU5Nzc1MzUw*_ga_9J976DJZ68*MTY2MDk3NzYwNS4x