bump Cargo.toml to 1.9.0

Merge pull request async-rs#917 from async-rs/v1.8.0

v1.8.0

Merge pull request async-rs#902 from async-rs/v1.7.0

v1.7.0

Merge pull request async-rs#890 from async-rs/1-6-5

chore: release v1.6.4

Co-authored-by: Yoshua Wuyts <yoshuawuyts+github@gmail.com>

Merge pull request async-rs#845 from async-rs/1-6-3

Merge pull request async-rs#814 from async-rs/1-6-1

chore: release v1.6.1

Merge pull request async-rs#794 from async-rs/1-6-0

Merge pull request async-rs#790 from async-rs/1-6-0-beta-2

Merge pull request async-rs#765 from async-rs/feat/1-6-0