Raise error when an unversioned schema is used

Why are we doing this work?

In Use versioned schemas when validating security ... (#353997 - closed) we made sure to use versioned security report schemas when possible. After we enable enforce_security_report_validation we don't want to ingest reports that don't conform to schema

Implementation plan

1. Adjust Gitlab::Ci::Parsers::Security::Validators::SchemaValidator#schema_path to error out if enforce_security_report_validation is enabled and no version is declared in the report