CI: fix version of OSX runner

[gaelicWizard]

Description

Now that Mac OS X is "version 11", the "minor" version is no longer relevant.

Alsö, clean up the run conditions.

Motivation and Context

We've been running on the initial-release version for months.

How Has This Been Tested?

All tests pass.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.
• If my change requires a change to the documentation, I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• If I have added a new file, I also added it to clean_files.txt and formatted it using lint_clean_files.sh.
• I have added tests to cover my changes, and all the new and existing tests pass.

[gaelicWizard]

...someone click click re-run on the failed job...it's so slow that the second incremented during the test...