CI (macos): Query installation prefix of Homebrew #609

Job	Run time
msvc (cl with OpenMP without CUDA, both)	38m 7s
ubuntu (gcc with CUDA, both)	1h 40m 24s
msvc (cl without OpenMP without CUDA, both)	48m 14s
ubuntu (gcc without CUDA, both)	1h 39m 28s
msvc (cl with OpenMP with CUDA, both)	1h 8m 55s
ubuntu (clang with CUDA, both)	1h 30m 44s
msvc (cl with OpenMP with CUDA, static)	1h 1m 41s
ubuntu (clang without CUDA, both)	1h 27m 4s
msvc (clang-cl with OpenMP without CUDA, both)	47m 11s
ubuntu (gcc with CUDA, static)	1h 38m 2s
	12h 19m 50s

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