[live-build] "W: Download is performed unsandboxed as root as file 'xxx'..."

[jnqnfe@gmail.com]

double checking some of my recent contributions with further test runs,
one of the issues on my todo list to look into is that when creation of
the source disc is turned on, I'm seeing the following for each source
package download:

```
Picking 'audit' as source package instead of 'libaudit-common'
NOTICE: 'audit' packaging is maintained in the 'Git' version control
system at:
https://salsa.debian.org/debian/audit.git
Please use:
git clone https://salsa.debian.org/debian/audit.git
to retrieve the latest (possibly unreleased) updates to the package.
Need to get 1143 kB of source archives.
Get:1 http://deb.debian.org/debian buster/main audit 1:2.8.4-3 (dsc)
[2483 B]
Get:2 http://deb.debian.org/debian buster/main audit 1:2.8.4-3 (tar)
[1124 kB]
Get:3 http://deb.debian.org/debian buster/main audit 1:2.8.4-3 (diff)
[16.7 kB]
Fetched 1143 kB in 1s (867 kB/s)
Download complete and in download only mode
W: Download is performed unsandboxed as root as file 'audit_2.8.4-
3.dsc' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13:
Permission denied)
```

note the troubling warning at the end.

with a lot to do I have not yet even determined whether this is a new
problem that has surfaced from my changes on master to the source
stage, specifically I made a change to have files downloaded to a new
empty folder rather the the root of chroot, so perhaps we need to
change the owner of that directory to satisfy apt/aptitude?, or whether
it already existed beforehand.

help solving this would be appreciated if anyone can get to an
understanding of the problem before I do.

thanks.