Ensures GitHub is available prior to downloading the runner

[simonbs]

The changes in this PR ensures that we do not attempt downloading the runner or setting up the runner until we have verified that the virtual machine is able to contact GitHub.

Failure to communicate with github.com, e.g. because the virtual machine did not have an Internet connection, would previously result in an error in the script, at which point the virtual machine would reboot. This could result in a boot loop if we were unable to communicate with github.com for a long period.

[xavierLowmiller]

Would you consider changing the test from a ping to something like curl -s https://github.com > /dev/null?
Today, I ran into an issue where curl works fine on Github, but ping doesn't, so this might be a bad proxy for detecting availability.

_{It's also what reddit suggests for similar issues (in more profane words)}

[simonbs]

@xavierLowmiller Sure! I didn't know about this issue. I won't have time to address it the next few days but I'm happy to review and merge a PR that fixes it 🙏

[xavierLowmiller]

Great! I'm happy to put one up ✌️