Exclude namespaces from the deprecated namespace linter

[robert-stuttaford]

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Describe the solution you'd like
I'd like to be able to exclude namespaces from the :deprecated-namespace linter.

Describe alternatives you've considered
We don't control the namespace in question (it's in hiccup), so we'd simply like to elide this warning from view, but without losing visibility on any other deprecated namespaces as that happens.