The Python provisioning on macOS ARM hosts is done multiple times
across separate targets.
This patch moves the code into a common script 'macos/python-arm.sh'.
As a drive-by, we bump the version of all targets to 3.12.11, whch is
the same as the one used in the macOS 15 ARM host.
Pick-to: 6.11 6.10 6.8
Change-Id: I8c1f6f7d635fe47b9faa34dbe6988e89252dc2c9
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
