[SecurityBundle] Fix typo in the check_path validator

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #3005, #2954
| License       | MIT

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 `Dependency Injection` 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.

It looks like it's better to create new class for `SecurityExtension` tests.