patch 8.1.1683: dictionary with string keys is longer than needed

Problem:    Dictionary with string keys is longer than needed.
Solution:   Use *{key: val} for literaly keys.
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 9064245..574beb5 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -280,6 +280,10 @@
   call assert_equal(expected, d.func(string(remove(d, 'func'))))
 endfunc
 
+func Test_dict_literal_keys()
+  call assert_equal({'one': 1, 'two2': 2, '3three': 3, '44': 4}, *{one: 1, two2: 2, 3three: 3, 44: 4},)
+endfunc
+
 " Nasty: deepcopy() dict that refers to itself (fails when noref used)
 func Test_dict_deepcopy()
   let d = {1:1, 2:2}