Minor release: Support for python 3.9, bug fixes, improved CI

Changes

• Sync back with master @bouthilx (#496)

🚀 Features

• Add support for python 3.9 @bouthilx (#497)

🐛 Bug Fixes

• Use SoftFileLock if FS doesn't support global lock @bouthilx (#506)
• Fix algorithm requirements backward @bouthilx (#498)

🧰 Maintenance

• Add isort @bouthilx (#505)
• Add black checks and remove flake8 @bouthilx (#504)
• Fix drafter config @bouthilx (#502)
• Test release drafter @bouthilx (#501)
• Add release drafter @bouthilx (#499)