Provision Python 2 for arm macs in CI

Latest version of macOS 12.3 removed python2.

See initial report here https://bugreports.qt.io/browse/QTBUG-101745

WebEngine 5.15 and 6.2 require python2, and won't work with python3.

Homebrew does not provide a Python2 package, and packages from python.org are intel-only.

We currently don't seem to provision any python2 for arm macs, compared to intel macs, and rather rely on the system installed python2.

arm
https://github.com/qt/qt5/blob/dev/coin/provisioning/qtci-macos-12.0-arm/25-python2.sh
intel
https://github.com/qt/qt5/blob/dev/coin/provisioning/common/macos/python2.sh

We should provision a version of python2 for the arm macs, otherwise webengine will likely fail to build whenever the arm mac machines are upgraded to 12.3.

Possible choices:
1) Try out if the intel package from python.org works with rosetta
2) Build with pyenv
3) Build from source