docs: clarify application of HOMEBREW_ARTIFACT_DOMAIN

[UiP9AV6Y]

bottle URLs are treated differently than any other URL.
this change clarifies the resulting URLs in the manpage.

closes #13222

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[UiP9AV6Y]

in addition to the docs update, i have also migrated the test cases from #13258

[MikeMcQuaid]

Thanks again @UiP9AV6Y!