Closes#17512
One of the changes of the Oxide API in 4.1 is that it now emits the
input CSS file itself as a dependency. This was fine in most of our
testing but it turns out that certain integrations (in this case a Qwik
project) don't like this and will silently crash with no CSS file being
added anymore.
This PR fixes this by making sure we don't add the input file as a
dependency on itself and also adds an integration test to ensure this
won't regress again.
## Test plan
- Tested with the repro provided in #17512
- Added a minimal integration test based on that reproduction that I
also validated will _fail_, if the fix is reverted.
