Update dependencies and fix imports in conftest.py

[Samk13]

❤️ Thank you for your contribution!

Description

• Fix breaking tests: In conftest.py, the testing mock utility from moto import mock_s3 has been updated to mock_aws. as mock_s3 is been deprecated and breaking tests.
• Dependency Update: In setup.cfg, the dependency pytest-black has been replaced with pytest-black-ng, and the Sphinx version constraint has been relaxed from a fixed version ==4.2.0 to >=4.2.0.
• Code Modernization: Removal of from future import. This indicates a move away from Python 2 compatibility layers, transitioning to Python 3 as the minimum supported version.

Checklist

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[utnapischtim]

Overall looks good to me.
NOTE: you could update the github/actions in the tests.yml and pypi-publish.yml file as in this commit. this prevents warnings for usage of node12 or node14

[tmorrell]

Looks good, thanks!