Add a scheduled GitHub Action to check upstream version

[jlaine]

Twice a day, a scheduled action checks the latest upstream release and compares it to the current phonenumbers version. The check succeeds if and only if the two versions match.

See #273

[jlaine]

Notes:

• I don't know what your "home" timezone is, so feel free to suggest a more convenient time
• I have included the "workflow_dispatch" trigger so the action can be run manually
• So far I've only witness manually triggered runs, I'm not sure if this is because I'm operating on a fork

Here is a scheduled run of the action:

https://github.com/jlaine/python-phonenumbers/actions/runs/5642100157

[daviddrysdale]

Looks good, thank you – just a couple of minor nits.

[jlaine]

Thanks to @AA-Turner for all the suggested changes!

I think I've addressed all the requested changes, I'd still value your input on whether you want to keep the workflow_dispatch.

[daviddrysdale]

Thanks @jlaine and @AA-Turner !

[jlaine]

Oh crud. The if github.repository_owner == "daviddrysdale" broke the build:

https://github.com/daviddrysdale/python-phonenumbers/actions/runs/5644422744

[daviddrysdale]

Yeah, it seems that an if: line uses GitHub expression syntax, not YAML syntax, and so strings need to be single quoted. No worries, easy to fix.