patch 8.2.1730: Vim9: cannot use member of unknown type

Problem:    Vim9: cannot use member of unknown type.
Solution:   When type is unknown us "any". (closes #6997)

src/testdir/test_vim9_assign.vim

@@ -676,6 +676,33 @@ def Test_assign_dict()
   assert_equal({'0': 0, '1': 1, '2': 2}, nrd)
 enddef
 
+def Test_assign_dict_unknown_type()
+  let lines =<< trim END
+      vim9script
+      let mylist = []
+      mylist += [#{one: 'one'}]
+      def Func()
+        let dd = mylist[0]
+        assert_equal('one', dd.one)
+      enddef
+      Func()
+  END
+  CheckScriptSuccess(lines)
+
+  # doesn't work yet
+  #lines =<< trim END
+  #    vim9script
+  #    let mylist = [[]]
+  #    mylist[0] += [#{one: 'one'}]
+  #    def Func()
+  #      let dd = mylist[0][0]
+  #      assert_equal('one', dd.one)
+  #    enddef
+  #    Func()
+  #END
+  #CheckScriptSuccess(lines)
+enddef
+
 def Test_assign_lambda()
   # check if assign a lambda to a variable which type is func or any.
   let lines =<< trim END

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1730,
 /**/
     1729,
 /**/

src/vim9compile.c

@@ -5080,12 +5080,14 @@ compile_assignment(char_u *arg, exarg_T *eap, cmdidx_T cmdidx, cctx_T *cctx)
 			}
 			else
 			{
-			    // An empty list or dict has a &t_void member,
+			    // An empty list or dict has a &t_unknown member,
 			    // for a variable that implies &t_any.
 			    if (stacktype == &t_list_empty)
 				lvar->lv_type = &t_list_any;
 			    else if (stacktype == &t_dict_empty)
 				lvar->lv_type = &t_dict_any;
+			    else if (stacktype == &t_unknown)
+				lvar->lv_type = &t_any;
 			    else
 				lvar->lv_type = stacktype;
 			}