[backport#12075] [scripts] Add missing univalue file to copyright_header.py

Summary:
415f86c6ae [scripts] Add missing univalue file to copyright_header.py (fanquake)

Pull request description:

This needs to be added so that PRs like #12062 don't modify the subtree.

Backport of Core PR12075

Test Plan:

./contrib/devtools/copyright_headers.py update .

check that the univalue thing did not get updated

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D8179