Fix Flake8 warning on test_invalid_url

tests/test_errors.py

@@ -146,7 +146,7 @@ def test_invalid_url():
  message = "File format not supported"
  with pytest.raises(Exception, match=message):
  url = camelot.read_pdf(url)
- assert is_url(url) == False
+ assert is_url(url) is False
 
 
 def test_ghostscript_backend_import_error(testdir):