[backport#14785] Scripts: Fix detection of copyright holders
Summary:
af9a9918b2 Fix detection of copyright holders (Cornelius Schumacher)
Pull request description:
Fix copyright holder detection so that `copyright_header.py report` creates a clean and accurate report: * Fix list of copyright holders in the code * Also detect copyrights which have a comma after the date * Exclude directories which are git subtrees
Backport of Core PR14785
Test Plan:
run it, check results
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D9114