runtime(dune): use :setl instead of :set in ftplugin

closes: #11419

Signed-off-by: Dani Dickstein <daniel.dickstein@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/dune.vim b/runtime/ftplugin/dune.vim
index 6e20a8f..7608d53 100644
--- a/runtime/ftplugin/dune.vim
+++ b/runtime/ftplugin/dune.vim
@@ -6,13 +6,14 @@
 "              2023 Aug 28 - Added undo_ftplugin (Vim Project)
 "              2018 Nov 03 - Added commentstring (Markus Mottl)
 "              2017 Sep 06 - Initial version (Etienne Millon)
+"              2024 Nov 09 - use setl instead of :set
 
 if exists("b:did_ftplugin")
   finish
 endif
 let b:did_ftplugin=1
 
-set lisp
+setl lisp
 
 " Comment string
 setl commentstring=;\ %s