.github: Update the path used for the homebrew LLVM install on macOS

Pull Request: https://github.com/freebsd/freebsd-src/pull/1212

(cherry picked from commit 1091f525df9d74f07d707d8a79a91fe26a6c50e3)
(cherry picked from commit f4b6272a26da7b1cf577d13c74c9f146412bad56)