Dependency on attrs package should be explicit

[bluetech]

Hi, I'm one of the pytest maintainers.

I am working on a PR to pytest that will remove the attrs dependency. This means that plugins that use attrs but do not explicitly require it will break. From a search among pytest plugins, I found that pytest-mock-resources is one such plugin.

attrs is used in this file: https://github.com/schireson/pytest-mock-resources/blob/d522be82cd3a08b886fb504429b315f30d7280eb/src/pytest_mock_resources/patch/redshift/mock_s3_copy.py

[bluetech]

The pytest PR is this: pytest-dev/pytest#10669

[DanCardin]

Thanks for the report! The use of attrs there is really unnecessary anyways

[DanCardin]

v2.6.7 wont have this defect