Update rstest dev-dependency to 0.26

[musicinmybrain]

Updates rstest to the latest release. Since rstest is just a dev-dependency for a trivial doctest, the very minor incompatibilities across rstest versions are not relevant, and I confirmed that cargo test still passes. I updated Cargo.lock using cargo update rstest.

[wiktor-k]

This looks good in general 👌

Two issues that the CI reported: missing sign off (see CONTRIBUTING.md) and some issue with the deny plugin. I see it has a v2 now. If you want to try to adjust it, you could do that in this PR. If not, I can do that later and then we rebase this PR.

Anyway, thanks for your contribution! 👋

[musicinmybrain]

I’ve added the signoff and attempted to update the deny plugin. We’ll see if it works.

[musicinmybrain]

I updated futures-* crates in Cargo.lock, since a local cargo deny check complained about yanked futures-util 0.3.30. (It looks like this upstream has the habit of yanking every releases but the current one: https://crates.io/crates/futures-util/versions)

[wiktor-k]

It looks like this upstream has the habit of yanking every releases but the current one

Apparently it's by design and all these old releases were buggy:

rust-lang/futures-rs#2502

https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md

Oh, well.

PR looks great - merging. Thanks again for your time and see you later!