For the slint! macro, we need to lookup files in the manifest path.
The base_directory function regressed in commit 0ff8e2c.
This was not cought by the test because it had falled back to the `pwd`
with a warning, as we used to load ressources relative to `pwd` as a
fallback.
So also check that there are no warning (meaning updating the rest of
the test so that there isn't any warnings)
Fix#4045
NOTE: This library is an internal crate of the Slint project.
This crate should not be used directly by applications using Slint.
You should use the slint crate instead.
WARNING: This crate does not follow the semver convention for versioning and can
only be used with version = "=x.y.z" in Cargo.toml.