patch 8.2.1301: Vim9: varargs argument type not parsed properly

Problem:    Vim9: varargs argument type not parsed properly.
Solution:   Skip over the "...". (issue #6507)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index ade1fd1..0d39d57 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -363,6 +363,19 @@
     assert_equal(123, g:echo)
   END
   CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    vim9script
+    def EchoList(...l: list<number>)
+      g:echo = l
+    enddef
+    let Funcref: func(...list<number>) = function('EchoList')
+    Funcref()
+    assert_equal([], g:echo)
+    Funcref(1, 2, 3)
+    assert_equal([1, 2, 3], g:echo)
+  END
+  CheckScriptSuccess(lines)
 enddef
 
 let SomeFunc = function('len')