Update supported macOS for self hosted agents

[tbegeberg]

The current documentation for self hosted agents supported macOS seems to be outdated, and added 14.0,.

[prmerger-automator[bot]]

@tbegeberg : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[Court72]

@steved0x

Can you review the proposed changes?

When the changes are ready for publication, add a #sign-off comment to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged" @MicrosoftDocs/public-repo-pr-review-team

[steved0x]

#sign-off