lint tests

Lint with [refurb](https://github.com/dosisod/refurb) using `--disable 126 --python-version 3.9`

Also update bats to 1.8.2 and bats-assets to 2.1.0. No changes to the tests, all still passing.

tests/test_downloader.py

@@ -152,7 +152,7 @@ def test_download_submission_hash_exists(
     RedditDownloader._download_submission(downloader_mock, submission)
     folder_contents = list(tmp_path.iterdir())
     output = capsys.readouterr()
-    assert len(folder_contents) == 0
+    assert not folder_contents
     assert re.search(r'Resource hash .*? downloaded elsewhere', output.out)