Fix sitemap XML header

[s-thom]

Motivation and Context

The XML header for the sitemap was missing a ?. I'm good at my job, I swear.

Screenshots (if appropriate)

Checklist

• [x] Text content in this PR was created by a human and not AI.
• [x] I have read the contribution guidelines and code of conduct.

[vercel[bot]]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated
ourflags-lgbt	✅ Ready (Inspect)	Visit Preview	Mar 17, 2023 at 6:36AM (UTC)