Use explicit module for Rails::HealthController

[p8]

This makes sure it falls under the "Rails" section of the API sidebar instead of its own section.

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[zzak]

IMO this is a bug in RDoc, there are a few places this can occur, and first noticed it when trying to deal with the Rails::Rails::Conductor mess.

But only this and RaiseWarnings actually show up at the top-level, I think they are worth fixing this way.

[p8]

But only this and RaiseWarnings actually show up at the top-level, I think they are worth fixing this way.

RaiseWarnings is a top level class though, so it makes sense to have it at the top level I guess.
Not sure if it could be namespaced under ActiveSupport::Testing instead.
cc @byroot

[byroot]

Yeah, good point. It should be nodoc, and we can move it under a namespaces, but the later doesn't matter as much because it's not shipped with the gem.