Hide ResourceWarning when running rbt post
We often run rbt post in an environment with environment variables PYTHONWARNINGS=default to help discover errors. This spits a lot of subprocess errors when running.

ResourceWarning: Enable tracemalloc to get the object allocation traceback
/usr/local/Cellar/python@3.9/3.9.4/Frameworks/Python.framework/Versions/3.9/lib/python3.9/subprocess.py:765: ResourceWarning: unclosed file <_io.BufferedReader name=13>
  _cleanup()

These errors stop showing up in unit tests and in rbt post in a private git repo.