When a module rejects a piece of media we end up trying to close the
same logging context twice.
Instead of fixing the existing code we refactor to use an async context
manager, which is easier to write correctly.
During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
This stops media (and thumbnails) from being accessed from the
listed domains. It does not delete any already locally cached media,
but will prevent accessing it.
Note that admin APIs are unaffected by this change.
