Revert to using macOS 12 for VR tests

[rmccar]

What is the context of this PR?

Fixes: #3159

Github seems to have recently updated their macos-latest runner to use macOS 14 (as explained here April 24 - https://github.blog/changelog/2024-01-30-github-actions-macos-14-sonoma-is-now-available/). These runners use the new Apple silicon CPUs which are currently incompatible with running colima (abiosoft/colima#970) which is what we use to run our VR tests.

This PR specifies that we use macOS 12 rather than "Latest".

How to review this PR

• Check the VR tests on another PR see the colima error
• See that the VR tests run and pass on this PR

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