patch 9.0.0836: wrong error when using extend() with funcref

Problem:    Wrong error when using extend() with funcref.
Solution:   Better check the variable type. (closes #11468, closes #11455)
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 938a839..831a894 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -2938,6 +2938,25 @@
   let g:bar = 123
   call extend(g:, #{bar: { -> "foo" }}, "keep")
   call assert_fails('call extend(g:, #{bar: { -> "foo" }}, "force")', 'E704:')
+  unlet g:bar
+
+  call assert_fails('call extend(l:, #{foo: { -> "foo" }})', 'E704:')
+  let bar = 123
+  call extend(l:, #{bar: { -> "foo" }}, "keep")
+  call assert_fails('call extend(l:, #{bar: { -> "foo" }}, "force")', 'E704:')
+  unlet bar
+
+  call assert_fails('call extend(g:, #{foo: function("extend")})', 'E704:')
+  let g:bar = 123
+  call extend(g:, #{bar: function("extend")}, "keep")
+  call assert_fails('call extend(g:, #{bar: function("extend")}, "force")', 'E704:')
+  unlet g:bar
+
+  call assert_fails('call extend(l:, #{foo: function("extend")})', 'E704:')
+  let bar = 123
+  call extend(l:, #{bar: function("extend")}, "keep")
+  call assert_fails('call extend(l:, #{bar: function("extend")}, "force")', 'E704:')
+  unlet bar
 endfunc
 
 func Test_funcref_to_string()
diff --git a/src/testdir/test_let.vim b/src/testdir/test_let.vim
index 3f9bdd4..4e4a386 100644
--- a/src/testdir/test_let.vim
+++ b/src/testdir/test_let.vim
@@ -316,6 +316,7 @@
   call assert_fails('let l += 2', 'E734:')
   call assert_fails('let g:["a;b"] = 10', 'E461:')
   call assert_fails('let g:.min = function("max")', 'E704:')
+  call assert_fails('let g:cos = "" | let g:.cos = {-> 42}', 'E704:')
   if has('channel')
     let ch = test_null_channel()
     call assert_fails('let ch += 1', 'E734:')