GHA: Try switching to old Xcode for macOS-13 jobs

[kinke]

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Testing this PR locally

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[ibuclaw]

At some point Xcode 14 will be unavailable, so this is just prolonging the inevitable - someone who is intimate with OSX and dmd back-end needs to:

1. Fix this issue in the compiler.
2. Fix all other issues targeting OSX whilst we're at it.
3. Fix debugging on OSX (with lldb/gdb).

[kinke]

There's an extra disadvantage - this workaround would need to be duplicated in the Phobos YAML.