patch 8.2.2168: Vim9: error for assigning to dict of dict

Problem:    Vim9: error for assigning to dict of dict.
Solution:   Remember the destination type. (closes #7506)

src/testdir/test_vim9_assign.vim

@@ -560,6 +560,12 @@ def Test_assignment_dict()
   dict3.key = 'yet another'
   assert_equal(dict3, {key: 'yet another'})
 
+  # member "any" can also be a dict and assigned to
+  var anydict: dict<any> = {nest: {}, nr: 0}
+  anydict.nest['this'] = 123
+  anydict.nest.that = 456
+  assert_equal({nest: {this: 123, that: 456}, nr: 0}, anydict)
+
   var lines =<< trim END
     vim9script
     var dd = {}