Fix Python Issues Flagged by pre-commit

[Matthew-Grayson]

🗣 Description

.github Changes

Integrate .env file into test_python job in backend.yml. This enables us to remove the public/private keys in mitmproxy_sign_requests.py and test_mitmproxy_sign_requests.py.
Note: this is a test RSA private key and not used in any deployed environment.

Other Changes

• Remove private/public keys from mitmproxy_sign_request.py and mitmproxy_sign_request.py
• Add error handling and timeout to get requests in cities.py and counties.py
• Configure bandit to skip rule B101, "assert used", for test files
• Configure flake8 to skip checking for docstrings in test files
• Add docstrings to all other python modules and functions
• Remove unused imports and variables
• Organize/alphabetize libraries in requirements.txt files and imports.
• Add types-requests to additional_dependencies for mypy.
• Update Scrapy to address security vulnerability.

💭 Motivation and context

Closes issue #77
All python-related pre-commit hooks now pass.

🧪 Testing

Unit tests pass.
The following pre-commit checks pass:

• bandit
• black
• flake8
• isort
• mypy
• pyupgrade
• requirements-txt-fixer

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.

✅ Pre-merge checklist

• Revert dependencies to default branches.
• Finalize version.

✅ Post-merge checklist

• Create a release.

[cduhn17]

LGTM

[dav3r]

I noted a few things that should be taken care of before I can approve this PR, as well as a couple of things that don't apply to this PR specifically, but I felt I should mention.

[dav3r]

Thanks for taking care of the items that I mentioned - looks good now! 👍

Approved with same caveat as #32:

@Matthew-Grayson stated that the remaining automated test failures will be addressed in future PRs.

[Matthew-Grayson]

@dav3r Of Course!