Reword the issue comment to use denylist instead of blacklist

[richo]

Changes the comment left on github issues to read:

⚠️ If you notice any spurious failure [please add them to the denylist](https://github.com/rust-lang/crater/blob/master/config.toml)!

Which I think is more inclusive than the old message which referred to it as a blacklist. Conveniently, the config file in question doesn't use that term so I don't think it will be confusing to anyone trying to figure out how to drive it.

While making this change crater still uses blacklist a lot internally, but that seemed like kind of a lot for a driveby PR, but if you'd take the patch I'd be happy to switch it out.

[BenjaminBrienen]

What's wrong with the word? The term doesn't seem to originate from anything to do with racism.

https://en.wikipedia.org/wiki/Blacklist_(computing)

[richo]

While there may or may not be a racial component, I think at this point it's not a hard sell that using other terms is more inclusive and more descriptive. Nothing about the terms whitelist or blacklist tells you which one allows or denies unless you happen to know which colour means which.