Fix CI build job in Ubuntu

[savetheclocktower]

This seemed to get things unstuck in #1308, so I'm opening this against master now.

This is the simplest possible thing that could possibly work: updating the location of buster packages now that Debian has archived them. Whether we should be moving to a newer baseline is above my pay grade.

[DeeDeeG]

Yes, this makes sense to me for now. Least possible change to separate concerns between "get builds going" vs "decide migration plan if any from old Debian distro for Linux bin building"

Thanks again for doing this! I completely forgot about archive.debian.org being a thing you could move to after EOL where needed. Though I've done it before for personal tinkering many moons ago. Checks out!

CI looks happy, packages can be gotten from archive.debian.org just fine it looks like!

Context for posterity: This is only needed in this workflow file where we deliberately use and old Debian Docker image for old glibc and thus compatibility with some older distros (when building our x64 Linux Pulsar binaries), particularly at the request of some RHEL-alike distro users.

[DeeDeeG]

This seemed to get things unstuck in #1309

I presume this means #1308?

[savetheclocktower]

Ehh, I'm not precise. You got the idea!