patch 8.2.3230: Vim9: type error when function return type is not known yet

Problem:    Vim9: type error when function return type is not known yet.
Solution:   When return type is unknown, use "any". (closes #8644)

src/testdir/test_vim9_builtin.vim

@@ -1172,6 +1172,16 @@ def Test_get()
   var F: func = function('min', [[5, 8, 6]])
   F->get('name')->assert_equal('min')
   F->get('args')->assert_equal([[5, 8, 6]])
+
+  var lines =<< trim END
+      vim9script
+      def DoThat(): number
+        var Getqflist: func = function('getqflist', [{id: 42}])
+        return Getqflist()->get('id', 77)
+      enddef
+      assert_equal(0, DoThat())
+  END
+  CheckScriptSuccess(lines)
 enddef
 
 def Test_getbufinfo()

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3230,
 /**/
     3229,
 /**/

src/vim9compile.c

@@ -2130,6 +2130,9 @@ generate_PCALL(
 	    }
 	}
 	ret_type = type->tt_member;
+	if (ret_type == &t_unknown)
+	    // return type not known yet, use a runtime check
+	    ret_type = &t_any;
     }
     else
     {