Mac-OS 12 runner image inconsistency: some use Python 2 instead of Python 3 when using shell: python

[Release-Candidate]

Description

Some Mac-OS 12 runner images changed the Python version used by shell: python from 3 to 2:

Broken image:

Current runner version: '2.311.0'
Operating System
  macOS
  12.7
  21G816
Runner Image
  Image: macos-12
  Version: 20230921.4
...
shell: /usr/local/bin/python {0}

Working image:

Current runner version: '2.311.0'
Operating System
  macOS
  12.6.9
  21G726
Runner Image
  Image: macos-12
  Version: 20231029.1
...
shell: /Library/Frameworks/Python.framework/Versions/Current/bin/python {0}

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 20.04
• Ubuntu 22.04
• macOS 11
• macOS 12
• macOS 13
• Windows Server 2019
• Windows Server 2022

Image version and build link

Runner Image
  Image: macos-12
  Version: 20230921.4

https://github.com/Release-Candidate/OCaml-Buck-2-Examples/actions/runs/6920546919/job/18825156355

Is it regression?

https://github.com/Release-Candidate/OCaml-Buck-2-Examples/actions/runs/6850661919/job/18625271291

Expected behavior

The Python version used by shell: python is consistently Python 3, the same as all other runners (ubuntu-latest, windows-latest).

Actual behavior

A Python 2 interpreter is used by shell: python in some MacOS 12 runner images.

Repro steps

Use this Runner:

Runner Image
  Image: macos-12
  Version: 20230921.4

Check the version of Python used by shell: python

[mikhailkoliada]

Duplicate of #8642