GitHub Action: Option to parse version from pyproject.toml

[srittau]

Is your feature request related to a problem? Please describe.

When using black's GitHub action "psf/black", you need to specify the black version to use manually as an option to the action, in addition to specifying it in pyproject.toml. This can easily lead to inconsistencies between the files, especially when using dependabot to keep the version current.

Describe the solution you'd like

It would be useful if the action could read the version to use from pyproject.toml. This would probably need a new option like "pyproject: true" to enable this behavior.

Describe alternatives you've considered

An alternative is to read pyproject.toml in a previous step in a GitHub workflow for example using SebRollen/toml-action, and provide the read value using a variable, but just using a flag to this action would be much easier and less error prone.