fix error in changelog

[braingram]

During conflict resolution a changelog error was introduced in: https://github.com/spacetelescope/stdatamodels/pull/281

This PR fixes the changelog by removing the extra <<<<<<< HEAD.

Checklist

• [ ] added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• [ ] updated relevant tests
• [ ] updated relevant documentation
• [ ] updated relevant milestone(s)
• [ ] added relevant label(s)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 64.92%. Comparing base (4d7c3a6) to head (5c4ad5a). Report is 11 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #282 +/- ## ========================================== + Coverage 64.84% 64.92% +0.08% ========================================== Files 103 104 +1 Lines 5694 5710 +16 ========================================== + Hits 3692 3707 +15 - Misses 2002 2003 +1 ```

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