[v1.4] Downgrade Python to 3.11 for macOS CI builds

[JonasVautherin]

Backporting #2179

[JonasVautherin]

Hmm CMake keeps detecting 3.12 🤔:

-- Found Python3: /usr/local/bin/python3.12 (found version "3.12.0") found components: Interpreter

I think that it works for the runner 20230921.1, but not for 20231029.1. Some changes there:

• CMake 3.27.6 -> 3.27.7
• Python 3.11.5 -> 3.12.0

I can't explain why it seems to work in main and not in v1.4 yet.

[JonasVautherin]

Oh, v1.4 uses CMake to detect Python:

find_package(Python3 COMPONENTS Interpreter REQUIRED)

main does not. Maybe something in this patch should be backported.

[julianoes]

I think this is missing: https://github.com/mavlink/MAVSDK/blob/04e78f163d3dd630103a353cca8d04fd943f8486/third_party/mavlink/mavlink.patch

[JonasVautherin]

Ok let's see. In the current CI run, iOS has the older runner image, and macOS has the new one. If your latest suggestion fixes it, both should work 👍.

[JonasVautherin]

Seems better! Good catch @julianoes!

[JonasVautherin]

Now Windows breaks 🙈. Retrying with set(Python_FIND_REGISTRY "NEVER") for Windows, which was the old value.