CI: Use new Ubuntu 22.04 image and remove deprecated Ubuntu 18.04

[bergmeister]

PR Summary

See below where Ubuntu 18.04 has been deprecated and will soon be removed. Also there are new Ubuntu 22.04 and macOS 12 images where the latest tag hasn't been updated to point to them. Therefore explicitly adding Ubuntu 22.04, which is better going forward but keep using macos-latest due to their high release frequency.
https://learn.microsoft.com/en-us/azure/devops/pipelines/agents/hosted

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.

[JamesWTruher]

@bergmeister - it does mean that every time a new MacOS is supported (or deprecated) we'll need to update this.

[bergmeister]

Yes but I'd rather be explicit and due to them always offering at least 2 versions, we'd always have to update at least the older version, same for Ubuntu. Also, latest doesn't point to macos 12 but 11 atm so we couldn't use it otherwise atm. But if you'd rather trade less maintenance for less coverage then that's ok as well.