tuned: fewer warnings in IntelliJ IDEA;

--- a/src/Pure/Admin/component_elm.scala	Sun Jan 12 13:27:47 2025 +0100
+++ b/src/Pure/Admin/component_elm.scala	Sun Jan 12 13:41:00 2025 +0100
@@ -12,7 +12,7 @@
   sealed case class Download_Platform(platform_name: String, file_name: String) {
     override def toString: String = platform_name
 
-    def archive_name = file_name + ".gz"
+    def archive_name: String = file_name + ".gz"
     def download(base_url: String, version: String): String =
       base_url + "/" + version + "/" + archive_name