fix(http1): is_timeout works on HeaderTimeout

[T-aian]

Changed hyper::Error::is_timeout() to also check if the kind of the error is a HeaderTimeout. I also added a test at the end of server.rs to check for this kind of timeout error.

Fixes #3780

[seanmonstar]

Thanks for the PR! Looks like rustfmt is grumpy. rustfmt --edition 2021 $(git ls-files '*.rs') should fix it up.

[seanmonstar]

Looks like the feature flag combinations are tricky. Here's what I'd suggest:

#[cfg(all(feature = "http1", feature = "server"))]
if matches!(self.inner.kind, Kind::HeaderTimeout) {
    return true;
}

self.find_source::<TimedOut>().is_some()