Cache macOS CI binaries #226

Job	Run time
Apache2 tests on Linux	2m 15s
C++ tests on macOS	4m 0s
Apache2 tests on macOS	2m 11s
C++ tests on Linux	1m 16s
Homebrew packaging tests	3m 59s
Nginx tests on Linux	2m 7s
Nginx tests on macOS	1m 53s
Nginx dynamic module tests on Linux	1m 0s
Nginx dynamic module tests on macOS	46s
Node.js tests on Linux	19s
Ruby tests on Linux	1m 0s
Node.js tests on macOS	1s
Source packaging tests	33s
Ruby tests on macOS	1s
Passenger Standalone tests on Linux	3m 5s
Passenger Standalone tests on macOS	1s
	24m 27s

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