backtrace problem on nightly

In a strange constellation I'm running into the following error:

```plain
error[E0308]: mismatched types
--> /Users/I563162/.cargo/registry/src/github.com-1ecc6299db9ec823/http-types-2.12.0/src/error.rs:114:18
|
114 | Some(backtrace)
| ---- ^^^^^^^^^ expected `&Backtrace`, found enum `std::option::Option`
| |
| arguments to this enum variant are incorrect
|
= note: expected reference `&Backtrace`
found enum `std::option::Option<&Backtrace>`
```

looking at the code:

https://github.com/http-rs/http-types/blob/6f38b3ea86602a8fa907c135373ff94400e11cd4/src/error.rs#L111-L118

I see no change in over 2 years. Also on the `anyhow` crate (`self.error` is of type `anyhow::Error`) I cannot see any change on the `backtrace()` method.

However a fix like this would solve the problem:

```patch
- let backtrace = self.error.backtrace();
+ let backtrace = self.error.backtrace()?;
```

## Things I've used:
- depdency tree to `http-types`:
```
http-types v2.12.0
├── async-h1 v2.3.3
│ └── tide v0.16.0
```
- `http-types` version `2.12.0`
- `anyhow` version `1.0.65`
- rust version
```sh
cargo --version && rustc --version
cargo 1.63.0-nightly (38472bc19 2022-05-31)
rustc 1.63.0-nightly (5435ed691 2022-06-07)
```

Start with src/error.rs lines 111-118, linked in the issue, and compare the backtrace type returned by anyhow 1.0.65 with the Rust nightly compiler behavior. Reproduce the error using the reported http-types 2.12.0 dependency setup and verify that the project compiles successfully with the corrected backtrace handling.

Written by the indexing model from the issue text.