Add cleanthat to spotless config

Author: blacelle

gradle/spotless.gradle

@@ -17,6 +17,7 @@ spotless {
 		java {
 			ratchetFrom 'origin/main'
 			bumpThisNumberIfACustomStepChanges(1)
+			cleanthat().version("2.4").sourceCompatibility("11").clearMutators().addMutators(['RSPEC-6212'])
 			licenseHeaderFile rootProject.file('gradle/spotless.license')
 			importOrderFile   rootProject.file('gradle/spotless.importorder')
 			eclipse().configFile rootProject.file('gradle/spotless.eclipseformat.xml')