master branch broken on 1.60.0-nightly

[smklein]

To repro:

$ rustup update
$ cargo build

Output:

error: could not compile `slack-chat-api` due to previous error
warning: build failed, waiting for other jobs to finish...
error: future cannot be sent between threads safely
   --> slack/src/lib.rs:425:5
    |
425 |     #[async_recursion]
    |     ^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: the trait `Sync` is not implemented for `core::fmt::Opaque`
note: future is not `Send` as this value is used across an await
   --> slack/src/lib.rs:433:66
    |
433 |                 bail!("status code: {}, body: {}", s, resp.text().await?);
    |                 -------------------------------------------------^^^^^^--
    |                 |                                                |
    |                 |                                                await occurs here, with `$crate::__export::format_args!($($arg)*)` maybe used later
    |                 has type `ArgumentV1<'_>` which is not `Send`
    |                 `$crate::__export::format_args!($($arg)*)` is later dropped here
    = note: required for the cast to the object type `dyn std::future::Future<Output = Result<FormattedMessageResponse, anyhow::Error>> + Send`
    = note: this error originates in the attribute macro `async_recursion` (in Nightly builds, run with -Z macro-backtrace for more info)

[jessfraz]

fixed and pinned