patch 8.2.1140: Vim9: return type of extend() is any

Problem:    Vim9: return type of extend() is any.
Solution:   Use type of the argument.

src/evalfunc.c

@@ -576,7 +576,7 @@ static funcentry_T global_functions[] =
     {"exp",		1, 1, FEARG_1,	  ret_float,	FLOAT_FUNC(f_exp)},
     {"expand",		1, 3, FEARG_1,	  ret_any,	f_expand},
     {"expandcmd",	1, 1, FEARG_1,	  ret_string,	f_expandcmd},
-    {"extend",		2, 3, FEARG_1,	  ret_any,	f_extend},
+    {"extend",		2, 3, FEARG_1,	  ret_first_arg, f_extend},
     {"feedkeys",	1, 2, FEARG_1,	  ret_void,	f_feedkeys},
     {"file_readable",	1, 1, FEARG_1,	  ret_number,	f_filereadable}, // obsolete
     {"filereadable",	1, 1, FEARG_1,	  ret_number,	f_filereadable},

src/testdir/test_vim9_func.vim

@@ -909,6 +909,15 @@ def Test_copy_return_type()
   assert_equal(6, res)
 enddef
 
+def Test_extend_return_type()
+  let l = extend([1, 2], [3])
+  let res = 0
+  for n in l
+    res += n
+  endfor
+  assert_equal(6, res)
+enddef
+
 def Line_continuation_in_def(dir: string = ''): string
     let path: string = empty(dir)
             \ ? 'empty'

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1140,
 /**/
     1139,
 /**/