@stephen-dexda pointed out in #341 that our update in #330 changed
the `chown` operation to apply to the entire `/data` directory,
rather than just `/data/packages`. For anyone who was previously
relying on a workflow like mounting a read-only secrets directory
into `/data` to host authentication information, this broke their
workflow.
This fix sets `entrypoint.sh` to only `chown` `/data/packages`, which
should ensure that the permissions issues resolved by #330 (e.g. #309)
remain fixed, while also fixing the issue in #341.
