patch 8.2.0659: Vim9: no test for equal func type

Problem:    Vim9: no test for equal func type.
Solution:   Add a test.  Improve type check.
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index ace3d2f..ef5c00c 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -30,6 +30,16 @@
   assert_equal('two', {} ? 'one' : 'two')
   var = 0
   assert_equal('two', var ? 'one' : 'two')
+
+  let Some: func = function('len')
+  let Other: func = function('winnr')
+  let Res: func = g:atrue ? Some : Other
+  assert_equal(function('len'), Res)
+
+  let RetOne: func(string): number = function('len')
+  let RetTwo: func(string): number = function('winnr')
+  let RetThat: func = g:atrue ? RetOne : RetTwo
+  assert_equal(function('len'), RetThat)
 enddef
 
 func Test_expr1_fails()