package_versions_from_directory needs test for conflict checking

I don't have the time to make a test for this right now, thus i am documenting here what needs to be done:

In t/metadata.t the tests for package_versions_from_directory need to be extended by way of adding another file to the dist being inspected, said file needing to be stuck in a sub dir, e.g. Nested::Simple. The file should contain code sufficient to trigger the error of "Unexpected conflict in '$package'; multiple versions found.\n". Said throwing should be considered a success.

This needs to be tested because in its current state the path splitting a little further up would keep this check from functioning properly. I am providing a fix for this in a pull request to come, but a test will need to be made as per above.

Start in t/metadata.t with the existing package_versions_from_directory tests. Add a file in a nested subdirectory, such as Nested::Simple, with content that creates the stated package-version conflict; done means the test observes the expected Unexpected conflict in '$package'; multiple versions found. error.