Post macos 13 deprecation to readmes

[jasonkarns]

Description

Fix lax of documented deprecation

Fixes #13402

Related issue:

Check list

• Related issue / work item is attached
• Tests are written (if applicable)
• Documentation is updated (if applicable)
• Changes are tested and related VM images are successfully generated

[Marcono1234]

Not a member of this project, but I am wondering whether it would be better to use a GitHub Markdown Alert to make it stand out more than a regular announcement?

(though not sure if that, and also your change here, could break automation or would be automatically reverted again because those READMEs seem to be updated automatically)

[erik-bershel]

There's no need. Notifications are sent through a fairly large number of channels including GitHub blog, Azure DevOps blog, public repo announcement, brownouts and launch annotations, and they're no longer relevant due to the official end of the process.

[jasonkarns]

I disagree strongly.

As it stands, a user who goes to the readme today has absolutely no indication that the runner is disabled. If that runner is no longer available, why does the readme exist? If it's deprecated, why is there no notice? This is extremely contradictory and hostile user experience. "here's a readme for a runner that no longer works, and we also we won't indicate anything to that effect. lol"