Clean up CSSOptimizer unit test.

tanushree gupta → made their first commit to this issue’s fork.

I've removed the provided lines
Kindly review

Needs a phpstan baseline update.

We've removed the `file_uri_scheme()` mock from the test as requested. After doing that, the test is now throwing a 500 error — likely because the function isn't available in the test context anymore.
We've updated the PHPStan baseline to reflect the current state.

Just wanted to check how you'd prefer we handle this:

* Should we include the required `file.inc` file manually in the test (using something like `require_once`)?
* Or would it make more sense to convert this into a `KernelTestBase` or another test type where the function is already available?
* Or is it okay to leave things as they are now with the updated baseline?

file_uri_scheme() was removed a long time ago. the test fail is unrelated, those tests just sometimes randomly fail. If it doesn't look related to your changes, you can trigger a retest. I did that now.

Thank you!!

Seems straight forward enough.