upgrade macos github CI to macos 14

[metagn]

Macos 12 gives a warning:

You are using macOS 12.
We (and Apple) do not provide support for this old version.
It is expected behaviour that some formulae will fail to build in this old version.
It is expected behaviour that Homebrew will be buggy and slow.
Do not create any issues about this on Homebrew's GitHub repositories.
Do not create any issues even if you think this message is unrelated.
Any opened issues will be immediately closed without response.
Do not ask for help from Homebrew or its maintainers on social media.
You may ask for help in Homebrew's discussions but are unlikely to receive a response.
Try to figure out the problem yourself and submit a fix as a pull request.
We will review it but may or may not accept it.

Apparently macos 14 is M1 so macos 13 is another option, as well as macos-14-large which is amd.

[metagn]

Some packages (arraymancer, weave, taskpools, asyncthreadpool, this test file from nimterop) seem to individually not support M1/ARM.

On our end, the C++ imported exceptions test in the manual seems to fail for some reason. I don't know why this would happen.

Opening new PR with macos-14-large instead.