Restrict collating_using_adder_collator test on feature real-overseer

[coriolinus]

This test can only pass given that feature, and runs forever otherwise.

This change ensure that a careless cargo test --all doesn't run forever.

[ordian]

Looks good, although I prefer
required-features annotation on a test
https://doc.rust-lang.org/cargo/reference/cargo-targets.html?highlight=required-features#configuring-a-target

example

[coriolinus]

If we used required-features, then no future tests in the same crate would run unless that feature were specified, which I think is not the behavior we'd expect and desire. I like the granularity of disabling only this single test in the event that it can't pass.

[edit]
Oh, I see, looks like we can specify the name of the test as well as required features. That's less a limitation then I'd thought, then. Even so, my instinct is to prefer the more local annotation.