Bump `bitreq` (pending new release)

[luisschwab]

rust-bitcoin/corepc#560

[oleonardolima]

FWIW it's valid to note that bitreq is only a dev-dependency, if anyone else is looking into the vulnerabilities raised by cargo audit job.

[oleonardolima]

The latest bitreq is a patch release, it should be resolved automatically, no need to bump it for now.