Update CODEOWNERS

[mrice32]

Motivation

Add David to codeowners.

Testing

Check a box to describe how you tested these changes and list the steps for reviewers to test.

• [ ] Ran end-to-end test, running the code as in production
• [ ] New unit tests created
• [ ] Existing tests adequate, no new tests required
• [ ] All existing tests pass
• [x] Untested

Issue(s)

N/A