Support for af-south-1

[mcameron]

I'd like to use agents in af-south-1. Agents are spinning up, however they're not registering with github.

Excerpt from /var/log/user-data.log on an agent:

Package git-2.32.0-1.amzn2.0.1.x86_64 already installed and latest version
Nothing to do
mkdir: cannot create directory ‘actions-runner’: File exists
download failed: s3://default-dist-xxxx1234/actions-runner-linux.tar.gz to ./actions-runner.tar.gz An error occurred (IllegalLocationConstraintException) when calling the GetObject operation: The af-south-1 location constraint is incompatible for the region specific endpoint this request was sent to.

I've created a corresponding PR for proposed fix:
#1204