patch 9.0.1924: LSP server message still wrongly handled (after 9.0.1922)

Problem:  LSP server message still wrongly handled (after 9.0.1922)
Solution: Handle 'method' messages properly, don't discard them, add
          tests.

closes: #13141

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/optionstr.c b/src/optionstr.c
index aeeab27..5fceb85 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -1858,7 +1858,7 @@
  * The 'jumpoptions' option is changed.
  */
     char *
-did_set_jumpoptions(optset_T *args)
+did_set_jumpoptions(optset_T *args UNUSED)
 {
     if (opt_strings_flags(p_jop, p_jop_values, &jop_flags, TRUE) != OK)
 	return e_invalid_argument;