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
Avoid using our own, potentially installed, curl for
the test reporting APIs in case it is broken.
Reviewed-by: Daniel Stenberg
Preparation for #6049Closes#6063
