chore: Fix cargo-deny configuration

[DataTriny]

Blocks #7

This makes cargo-deny stricter, but also more in line with the rest of the ecosystem.

[mwcampbell]

How much of this will we be applying to the main repo? Of course, this is the kind of thing that's annoying to maintain across multiple repos. But I think we had to do that split.

[DataTriny]

@mwcampbell I plan to basically copy this into the main repo, which will fix AccessKit/accesskit#349. We will be able to clean deny.toml a bit once AccessKit/accesskit#456 lands.

[DataTriny]

So it would make more sense to merge the zbus 4 PR first.

[DataTriny]

Here is the reason for the skipped dependencies:

• event-listener and event-listener-strategy: old async-channel version,
• syn: old thiserror version

In all cases we could get rid of them by updating the old crates in Cargo.lock.

[DataTriny]

This should be ready now.