Add `ffmpeg` for `doc_test_job` on CircleCI (#24397)

fix
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

.circleci/create_circleci_config.py

@@ -454,7 +454,7 @@ doc_test_job = CircleCIJob(
     "pr_documentation_tests",
     additional_env={"TRANSFORMERS_VERBOSITY": "error", "DATASETS_VERBOSITY": "error", "SKIP_CUDA_DOCTEST": "1"},
     install_steps=[
-        "sudo apt-get -y update && sudo apt-get install -y libsndfile1-dev espeak-ng time",
+        "sudo apt-get -y update && sudo apt-get install -y libsndfile1-dev espeak-ng time ffmpeg",
         "pip install --upgrade pip",
         "pip install -e .[dev]",
         "pip install git+https://github.com/huggingface/accelerate",