Summary:
https://github.com/yugabyte/yb-cpplint/pull/23 enforces a stricter
copyright format for C++ files.  D46750 fixes the violations on master,
but it will not be backported.  Instead, demote the lint rule to warning
level on backport branches.

Jira: DB-18295

Test Plan: Jenkins: skip, rebase: 2024.2

Reviewers: esheng, #db-approvers

Reviewed By: esheng, #db-approvers

Subscribers: rthallam, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D46785