[Debug] enhance non-PSR-0 compatibility for case mismatch test

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | no
| License       | MIT
| Doc PR        | no

Fix compatibility with non-PSR-0/4 loading schemes.
See https://github.com/symfony/symfony/pull/10201#issuecomment-35567573