ci: move OSX static build test to macos-12 env

GitHub shuts down the macos-10.15 virtual environments [1] and
the bug [2] is fixed. So it's time to move the OSX static build
testing to a newer environment.

[1] https://github.com/actions/virtual-environments/issues/5583
[2] https://github.com/tarantool/tarantool/issues/7459

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