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)

Author: brammool

src/testdir/test_vim9_func.vim

@@ -363,6 +363,19 @@ def Test_call_funcref()
     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')

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1301,
 /**/
     1300,
 /**/

src/vim9compile.c

@@ -1956,6 +1956,8 @@ skip_type(char_u *start, int optional)
 	    {
 		char_u *sp = p;
 
+		if (STRNCMP(p, "...", 3) == 0)
+		    p += 3;
 		p = skip_type(p, TRUE);
 		if (p == sp)
 		    return p;  // syntax error