prefer quiet mode: potentially more robust ssh connection, e.g. when master closes;

--- a/src/Pure/Tools/build_cluster.scala	Sun Sep 03 16:18:06 2023 +0200
+++ b/src/Pure/Tools/build_cluster.scala	Sun Sep 03 16:19:58 2023 +0200
@@ -171,7 +171,8 @@
           build_id = build_context.build_uuid,
           isabelle_home = remote_isabelle_home,
           afp_root = remote_afp_root,
-          dirs = Path.split(host.dirs).map(remote_isabelle.expand_path))
+          dirs = Path.split(host.dirs).map(remote_isabelle.expand_path),
+          quiet = true)
       remote_isabelle.bash(script).check
     }