Add CI on Julia 1.9 and fix Ubuntu builds for unsupported versions

[gdalle]

Julia versions 1.5 and 1.7 have not been supported for a while, so they didn't exist on Ubuntu 22.04

This was revealed by the update #305

Solution:

• run tests for 1.5 and 1.7 on Ubuntu 20.04
• run tests for 1.8 on Ubuntu 22.04
• run tests for the rest on Ubuntu latest, which for now is 22.04