Update CODEOWNERS: rename team-fm-next to team-fm-foundations (#209)

## Summary

Renames the CODEOWNERS team reference from `@launchdarkly/team-fm-next`
to `@launchdarkly/team-fm-foundations` to reflect the team's new name.
This is part of a batch update across multiple repos in the org.

## Review & Testing Checklist for Human
- [ ] Verify that the GitHub team `@launchdarkly/team-fm-foundations`
exists and has the expected members
- [ ] Confirm no other references to `team-fm-next` remain in this repo
outside of CODEOWNERS (e.g., CI configs, docs)

### Notes
- This repo's CODEOWNERS only had a single reference to the old team
name.
- Part of an org-wide rename affecting multiple repositories.

Link to Devin session:
https://app.devin.ai/sessions/8abe80d07e414755864c1b9c67215686
Requested by: @kparkinson-ld

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: kparkinson-ld

CODEOWNERS

@@ -1,3 +1,3 @@
 # These owners will be the default owners for everything in the repo.
 
-* @launchdarkly/team-fm-next
+* @launchdarkly/team-fm-foundations