Use a CI configuration fixture file to test YamlProcessor
This test for Gitlab::Ci::YamlProcessor currently uses the actual CE/EE .gitlab-ci.yml file to test that the processor validates correctly.
In a CI environment, this is a redundant test. If our config were invalid, the test wouldn't run.
In a local development environment, this test can still be useful to test that the class still behaves as expected while making changes. However, I'd expect us to be using a fixture file that isn't changed as frequently as our actual configuration, and which contains all the various configuration options that we'd want to ensure stay functional.
This test setup became an issue in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6259 where we tried to add include to our configuration, which is license-gated.
A simple quick fix would be copying our configuration file as it is to the spec/fixtures directory, and updating the test to use that.