Olddeps job is running against Python 3.8, but our oldest supported is 3.7

[DMRobertson]

At the time of writing we use the system version of python3 that's provided by Ubuntu focal, which is 3.8.

[DMRobertson]

Is there any particular reason that olddeps is tied to a particular Debian/Ubuntu distribution? What's there to stop us from using actions/setup-python with version: 3.7? I guess we wouldn't have older libcs...

Oh, it's the old postgres version we want. Hmm.

[richvdh]

for context, this change happened in #12343. It's not obvious to me if we realised that this would bring Python 3.8 at the time.

That said, we do have separate test runs for Python 3.7, so it's not necessarily a large problem.

[richvdh]

Oh, it's the old postgres version we want. Hmm.

I'm not sure it is. We have a separate test job for python 3.7 and postgres 10.

[DMRobertson]

Fixed as a drive-by in #13707, thanks Erik!