Set changelog job to run on iteration release

This MR prevents running the scheduled changelog pipeline every Friday, and instead every other Friday to align with our iteration cycle.

Reviewer Checklist:

• I, the Assignee, have run Axe tools on any updated pages, and fixed the relevant accessibility issues
• These changes meet a specific OKR or item in our Quarterly Plan.
• These changes work on both Safari and Chrome.
• These changes have been reviewed for Visual Quality Assurance and Functional Quality Assurance on Mobile, Desktop, and Tablet.
• These changes work with our Google Analytics and SEO tools.
• These changes have been documented as expected.

Closes: #1869 (closed)