Update `brew test-bot` to fail CI on any formula install failures

[scotttrinh]

At the moment, the test-bot command only seems to fail hard on linting errors, but if the install of the formulae fails, it inexplicably passes with a warning about the failures?! 😱

I think we want to add --fail-fast, but the only real way to test this is to ensure that the formulae are changed, so we'll need to do that in the context of another change/fix here, or figure out a way to test them even if they haven't changed.

[CarsonF]

I tried --fail-fast and it didn't do anything.