Patch issue with nullable attributes

[kabilar]

Description

• An error has recently surfaced when nullable attributes are not inserted. I am currently using the DataJoint MySQL Docker image in the Dev Container/Codespace environment. As a temporary solve, I propose inserting the null value.

Changes

• Insert a null value for package_version
• Update GitHub Actions workflows to new configuration. The commented sections will be uncommented when the Dev Container configuration is added in a future pull request.
• Update README to mirror updated instructions in other Elements
• Update version and changelog
• Format with black

[kabilar]

Version 0.2.11 has been tagged and released on GitHub, and published on PyPI.