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MINOR: [R] add some verbosity to homebrew tests

This doesn't resolve the brew issue (see https://issues.apache.org/jira/browse/ARROW-16070), but it makes it more obvious where and what is going wrong.

Closes #12750 from jonkeane/homebrew-verbose

Authored-by: Jonathan Keane <jkeane@gmail.com>
Signed-off-by: Jonathan Keane <jkeane@gmail.com>