The plugin looks for `settings.gradle` file only at https://github.com/devcon5io/mutation-analysis-plugin/blob/f82addfd34cef6dff399ce23d25cd1e5b4dd59df/src/main/java/ch/devcon5/sonar/plugins/mutationanalysis/sensors/ReportCollector.java#L71. Gradle made Kotlin the default DSL quite some time ago, so support for `settings.gradle.kts` and other `.gradle.kts` scripts is essential.