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
was discovered to be problematic while investigating an incident reported by
Von back in May. curl in this case doesn't include a Content-Length: or
Transfer-Encoding: chunked header which is illegal. This test case is
added to DISABLED until a solution is found.