[CI] Fix mypy for vllm/reasoning (#35742)

Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>
Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/entrypoints/openai/test_gptoss_structural_tags_integration.py

@@ -23,7 +23,7 @@ class TestGptOssStructuralTagsIntegration:
         """Create a mock tokenizer."""
         tokenizer = Mock()
         tokenizer.encode = Mock(return_value=[1, 2, 3, 4, 5])
-        tokenizer.vocab = {"<|end|>": 6}
+        tokenizer.get_vocab = Mock(return_value={"<|end|>": 6})
         return tokenizer
 
     @pytest.fixture