Check for [workspace] when finding workspace root

[mgeisler]

Before, the top-most Cargo.toml file was used. Now we use the nearest Cargo.toml file which contain a line saying [workspace].

This should avoid false positives when Cargo workspaces are nested inside each other: in this case, the inner package will have an empty [workspace] table.

[mgeisler]

Eh, ehm... This fails because the tests interact with each other: the first unit test will read the environment variable and cache it.

So this will need some other approach to be testable (an Integration test could work, but it doesn't have access to the private to_abs_ws_path function).

[bjorn3]

You could make an integration test which creates a file containing expect![], run it with the option to update the test expectation and then check if it is correctly updated.

[mgeisler]

You could make an integration test which creates a file containing expect![], run it with the option to update the test expectation and then check if it is correctly updated.

Ah, that's a good idea! I was shying away from that approach since I feared that I would need to call cargo test or similar... But I see now that I can trigger it all from the integration test. I've updated the commit accordingly.