patch 8.2.0623: typo in test comment

Problem:    Typo in test comment. (Christ van Willegen)
Solution:   Avoid mixing up a data structure with a body part.
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 2087f77..a2cc6b5 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -547,7 +547,7 @@
   call assert_equal({'a': 99, 'b': 100}, d)
 endfunc
 
-" Cannot use += with a locked dick
+" Cannot use += with a locked dict
 func Test_dict_lock_operator()
   unlet! d
   let d = {}