don't expect Diff Reference section in code_message if there are no c…

…hanges

tests/code_context_test.py

@@ -218,12 +218,10 @@ def func_4(string):
     mocker.patch.object(DefaultFilter, "filter", side_effect=filter_mock)
 
     code_message = await code_context.get_code_message(0, prompt="prompt")
-    assert count_tokens(code_message, "gpt-4", full_message=True) == 103  # Code
+    assert count_tokens(code_message, "gpt-4", full_message=True) == 95  # Code
     assert (
         code_message
         == """\
-Diff References: index (last commit)
-
 Code Files:
 
 file_1.py (search-result, user-included)