leaf-common 1.2.21

This is the first release attempt to publish leaf-common to pypi.

What's Changed

• UN-2902 Prepare for publishing on pypi. by @andreidenissov-cog in #109
• Tweaks to pyproject.toml in preparation for pypi publishing by @donn-leaf in #111
• Provide github actions to test and publish to pypi by @donn-leaf in #112

Full Changelog: 1.2.20...1.2.21