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
The list was freed incorrectly since the llist refactor of
cbae73e1dd959. Added test 1550 to verify that it works and avoid future
regressions.
Reported-by: Pascal Terjan
Fixes#1584Closes#1585
