(minor) Fix static init issue with Gradle multi-threaded resolve

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/KotlinProjectStructureMetadata.kt

@@ -80,7 +80,7 @@ sealed class SourceSetMetadataLayout(
     override fun toString(): String = name
 
     companion object {
-        private val values = listOf(METADATA, KLIB)
+        private val values get() = listOf(METADATA, KLIB)
 
         fun byName(name: String): SourceSetMetadataLayout? = values.firstOrNull { it.name == name }