Kept the Debian-based image at Bullseye.
For #24517.
# Checklist for submitter
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/Committing-Changes.md#changes-files)
for more information.
- [x] Manual QA for all new/changed functionality: Validated builds
(Docker and make) all work after this change, except for BitLocker
(requires Windows).
Ian Littman
07852b4c60