Bump isort to 5.12.0.

[0mdc]

Motivation and Context

Bump isort to 5.12.0.
The dependency was previously pinned at 5.11.5 due to dropped support of Python 3.7. We have since upgraded Habitat's python version. See facebookresearch/habitat-lab#1107.

How Has This Been Tested

Tested on CI.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.