Support for Parsing !reference Tag in GitLab CI YAML Files

[chussenot]

Hi everyone,

I recently submitted a pull request to add support for the !reference tag in GitLab CI YAML files. This tag is used extensively to optimize and reuse YAML content in GitLab CI pipelines, but it's currently not supported by the yaml-ast-parser, which causes issues when using Spectral for validation.

The MR adds this capability by allowing the AST parser to recognize and handle the !reference tag, whether it is used as a scalar or reference node. The goal is to improve compatibility with GitLab CI configurations.

It would be great to have a discussion around this and any feedback on the approach. Is there anyone else facing similar issues with Spectral's inability to handle !reference tags in GitLab YAML files?

Looking forward to your thoughts and feedback!