patch 8.2.0657: Vim9: no check if called variable is a FuncRef

Problem:    Vim9: no check if called variable is a FuncRef.
Solution:   Add a type check.
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 4632272..ace3d2f 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -213,6 +213,12 @@
   assert_equal(true, function('g:Test_expr4_equal', [123]) == function('g:Test_expr4_equal', [123]))
   assert_equal(false, function('g:Test_expr4_equal', [123]) == function('g:Test_expr4_is', [123]))
   assert_equal(false, function('g:Test_expr4_equal', [123]) == function('g:Test_expr4_equal', [999]))
+
+  let OneFunc: func
+  let TwoFunc: func
+  OneFunc = function('len')
+  TwoFunc = function('len')
+  assert_equal(true, OneFunc('abc') == TwoFunc('123'))
 enddef
 
 " test != comperator
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 4c821ec..bc1f873 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -345,6 +345,9 @@
   call CheckDefFailure(['let var: pam'], 'E1010:')
   call CheckDefFailure(['let var: sam'], 'E1010:')
   call CheckDefFailure(['let var: vim'], 'E1010:')
+
+  call CheckDefFailure(['let Ref: number', 'Ref()'], 'E1085:')
+  call CheckDefFailure(['let Ref: string', 'let res = Ref()'], 'E1085:')
 endfunc
 
 func Test_const()