fix: Fix sitemap so that if all feature flags are disabled, the build dosen't break

[nfpappas-oddball]

Description

broken next build sitemap

Ticket

This is to address a fix to the sitemap config

Developer Task

Tasks

Preview Give feedback

1. PR submitted against the main branch of next-build.
2. Link to the issue that this PR addresses (if applicable).
3. Define all changes in your PR and note any changes that could potentially be breaking changes.
4. PR includes steps to test your changes and links to these changes in the Tugboat preview (if applicable).
5. Provided before and after screenshots of your changes (if applicable).
6. Alerted the #accelerated-publishing Slack channel to request a PR review.
7. You understand that once approved, you are responsible for merging your changes into main. (Note that changes to main will move automatically into production.)

Testing Steps

tested in my local shell and it works as expected