feat: add CVE-2023-6879 to vulnerability allow list

Add CVE-2023-6879 to vulnerability allow list as the python-slim images we use don't have the fix for this and we do not do any video re-encoding.

I got this to run against one of the images affected by this vulnerability (had to fudge the schedule):

• pipelines/606152
• if you click on photo-api-base-py-3-11-container-scanning and then the Show complete raw, search for CVE-2023-6879, you can see that the vulnerabilities are now approved.

Closes #80