Pre-submission checks

• I am not reporting a bug (crash, false positive/negative, etc). These must be filed via the bug report template.
• I have looked through both the open and closed issues for a duplicate request.

What's the problem this feature will solve?

Dependabot now documents additional schedule.interval values (quarterly, semiannually, yearly, cron), but github-actions-models::dependabot::v2::Interval still only exposes daily/weekly/monthly. As a result, zizmor cannot parse repositories whose dependabot.yml uses the newer intervals or a cron expression, preventing audits on modern configurations.

Describe the solution you'd like

Extend the Interval enum to include the new documented variants (quarterly, semiannually, yearly, cron).

Additional context

GitHub documentation: https://docs.github.com/en/code-security/dependabot/working-with-dependabot/dependabot-options-reference#interval