Fix cross-project authorization test expectations

We implemented a couple of tests in manila-tempest-plugin that attempt to list or get an export location for a share that is not owned by a given user. These tests were expecting a 403 (unauthorized) exception, which is in line with manila’s current behavior.

However, such tests focus on a scenario that guesses the UUID of the share, meaning a 403 will confirm the existence of the resource.

The manila core code fixed that issue, so we need to adapt the tests to expect a 404 (Not found) exception instead.