fix(mistral): download all tokenizer files

Mistral required some vocab file that was not downloaded anymore, maing
the slow tests fail.

optimum/tpu/model.py

@@ -49,7 +49,7 @@ def fetch_model(
     local_path = snapshot_download(
         repo_id=model_id,
         revision=revision,
-        allow_patterns=["*.json", "model*.safetensors", SAFE_WEIGHTS_INDEX_NAME],
+        allow_patterns=["*.json", "model*.safetensors", SAFE_WEIGHTS_INDEX_NAME, "tokenizer.*"],
     )
     end = time.time()
     logger.info(f"Model successfully fetched in {end - start:.2f} s.")