poly check: a behaviour change when using the --strict option

[DavidVujic]

The poly check command has a behaviour change from version 1.25.0 of the Poetry plugin, and version 1.12.0 of the CLI.

In addition to the current functionality of the command, the library version strings across the workspace are now also checked when using it with the --strict option. The command will return an exit code 1 when there are version string mismatches.

Example:
Project A has version 0.109.2 of FastAPI defined in its pyproject.toml file.
The pyproject.toml of Project B has a different version added for FastAPI.

This will result in an exit code 1 (and a report) when using poly check --strict.

Implementation details in Pull Request #234