Bump copyright headers in tests (part2)
Summary:
Original script:
-BEGIN VERIFY SCRIPT- ./contrib/devtools/copyright_header.py update ./src/bench/ ./contrib/devtools/copyright_header.py update ./src/test/ -END VERIFY SCRIPT-
Partial backport of core PR15788:
https://github.com/bitcoin/bitcoin/pull/15788/commits/faf400077d0144363c2dd24187431d958fb149a9
Subset of test files only for ease of review.
Test Plan: Check nothing but core's copyright year changed.
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D5497