Use Ubuntu 22.04 in build workflow

[JohnathonMohr]

Description

GitHub started rolling out Ubuntu 24.04 over the last month, which our workflow picked up automatically by specifying ubuntu-latest as the Linux image name.

There is a breaking change between 22.04 (used previously) and 24.04 in which the mono software package is no longer installed on the image. (The note in the table at the link says software not available. dotnet still runs and builds without issue, so I don't quite fully understand the extent of it, but nuget commands aren't working without mono.)

This change pins Ubuntu to 22.04 while mono is missing from 24.04.

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