This is a rewrite of the previously used GPLv3+exception licensed
file. With this change, there is no more reference to GPL so we can
remove that from LICENSES/.
Ref: #9220Closes#9291
Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.
This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.
Closes#8869