Add note on macOS latest in GitHub hosted runners

[logankilpatrick]

Code of Conduct

• I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#github-hosted-runners

What part(s) of the article would you like to see updated?

Add a note at the bottom saying that -latest points to the latest available version which GitHub provides, not the latest available version open to the public. This is quite confusing and can lead to a situation as described below where you think you are running on the latest available OS but you are not.

Additional information

I also opened a discussion here: community/community#9052

[logankilpatrick]

Here's a quick poll (albeit not perfect science) which shows that many folks do not understand what macOS-latest points too: https://twitter.com/OfficialLoganK/status/1472231281429823493?s=20

[ramyaparimi]

@logankilpatrick
Thanks so much for opening an issue! I'll triage this for the team to take a look 👀

[lucascosti]

Apologies for the delay, @logankilpatrick! I'll quickly add a mention now