Fix exit code policy

Aligning expectation that "all repos succeed" means there are no repos with failures.

This brings back the old behavior from RunResults:

    if (reposWithFailures.isEmpty) ExitCode.Success else ExitCode.Error

See:
6259adb...9d9460a

modules/core/src/main/scala/org/scalasteward/core/application/ExitCodePolicy.scala

@@ -28,5 +28,5 @@ object ExitCodePolicy {
 
   val SuccessIfAnyRepoSucceeds: ExitCodePolicy = successIf(_.successRepos.nonEmpty)
 
-  val SuccessOnlyIfAllReposSucceed: ExitCodePolicy = successIf(_.reposWithFailures.nonEmpty)
+  val SuccessOnlyIfAllReposSucceed: ExitCodePolicy = successIf(_.reposWithFailures.isEmpty)
 }