ci(macos): install ccache when needed

[devjgm]

This change is 

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Codecov Report

Merging #6698 (c7c1247) into main (2211aeb) will not change coverage.
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@@           Coverage Diff           @@
##             main    #6698   +/-   ##
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  Coverage   95.69%   95.69%           
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  Files        1215     1215           
  Lines      112632   112632           
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  Hits       107784   107784           
  Misses       4848     4848           

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[devjgm]

Added install of pkg-config also, which vcpkg needs during the quickstart-cmake build

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[devbww]

I'm not sure what these idioms mean. If we fail to install pkg-config, we print its version?

[devjgm]

You're right that this is a bit strange. I'm mostly just following the established pattern that was already here. I think it's written like this because brew install <foo> commonly fails if foo is already installed but a newer version is available. It fails because we're told brew not to update packages (with HOMEBREW_NO_AUTO_UPDATE=1). But in the case of this failure, we want to proceed so we execute the command (that we think is installed) and prints its version. It's similar to || true, except that it will fail the the brew install fails for some other reason and the command actually does not exist.

Anyway, I think we may want to revisit the need for any of these brew commands now that we're running on more modern kokoro mac machines. We may be able to get rid of all of them (or many).