Fix compilation error on CI.

Author: nedtwigg

build.gradle

@@ -15,13 +15,13 @@ String VER_JUNIT_JUPITER = '5.9.2'
 subprojects {
 	apply from: 干.file('base/java.gradle')
 	apply from: 干.file('base/kotlin.gradle')
-	kotlin {
-		sourceSets.all {
-			languageSettings {
-				languageVersion = "2.0"
-			}
-		}
-	}
+//	kotlin {
+//		sourceSets.all {
+//			languageSettings {
+//				languageVersion = "2.0"
+//			}
+//		}
+//	}
 	apply from: 干.file('spotless/java.gradle')
 	apply plugin: 'java-library'