tuned signature: more permissive;

--- a/src/Pure/System/other_isabelle.scala	Wed Mar 27 12:54:43 2024 +0100
+++ b/src/Pure/System/other_isabelle.scala	Wed Mar 27 13:17:04 2024 +0100
@@ -33,8 +33,8 @@
   val isabelle_home: Path,
   val isabelle_identifier: String,
   isabelle_home_url: String,
-  ssh: SSH.System,
-  progress: Progress
+  val ssh: SSH.System,
+  val progress: Progress
 ) {
   other_isabelle =>