[SecurityBundle] Fix typo in the check_path validator

Actually, validator of `check_path` value is broken by #3005. It doesn't throw any exception even if `check_path` is an URI. 

I've faced with wrong tests class hierarchy: `SecurityExtensionTest` is abstract test and I have to create the same test configuration for every format: PHP, XML, YAML. It looks like we test `Config` and `Yaml` components. Issue with `check_path` does not depend on format, but such class hierarchy leaves me no choice. And I can't put test case into `ConfigurationTest`, because it doesn't know anything about security factories.

I probably have to remove test case, but it shows internal issue with tests.