Fix broken MacOS CI and switch to XCode's compiler

[camio]

The CI for MacOS broke again. Also, @dabrahams pointed out that it is unusual for Mac users to use the compiler distributed with brew so it would likely be more useful to test against the compiler distributed with XCode.

Acceptance Criteria

• The MacOS job works again.
• Change the job to use the stock compiler distributed with XCode instead of one in brew.

[camio]

Reopening because there was tech debt introduced with #470.

[dabrahams]

@camio I don't believe that's the case. The inconsistency is not new, just different. What is the new tech debt?
Also I opened #473 for that issue, which is not this issue. How does it serve anybody to have an issue titled “Fix broken MacOS CI and switch to XCode's compiler” when both of those tasks are done?

[camio]

We should probably discuss in the team meeting. It relates to our general "definition of done" for a task. Implicit acceptance criteria, in my mind, includes documentation/testing/and not knowingly introducing tech debt. In this case, the tech debt introduced is that we changed the version of the compiler from 13.0.1 to 13.0.0 and this line and this line were not updated to reflect that change.

[camio]

Closing this issue.